Functional Distinction Among PDC, LDH, and PDH in Pyruvate Metabolic Branches

Pyruvate is a key metabolic node at the end of glycolysis. Depending on redox status, oxygen availability, cell type, and metabolic demand, pyruvate can enter different metabolic branches. PDC, LDH, and PDH respectively represent three typical routes from pyruvate toward ethanol fermentation, lactate generation, and oxidative metabolism. Their core differences lie in carbon-flow direction, NADH reoxidation mode, energy yield, and metabolic regulatory significance.

Keywords: pyruvate; PDC; pyruvate decarboxylase; LDH; lactate dehydrogenase; PDH; pyruvate dehydrogenase; ethanol fermentation; lactate fermentation; acetyl-CoA; NADH; oxidative metabolism

1 Pyruvate as a Central Metabolic Node

1.1 Sources of Pyruvate

(1) End product of glycolysis

Glucose is converted into pyruvate through glycolysis, generating ATP and NADH at the same time. At this point, cells must continue to process pyruvate and NADH; otherwise, NAD⁺ supply in glycolysis becomes limited and glycolytic flux decreases.

(2) Sources from amino acid and organic acid metabolism

Alanine can be converted into pyruvate through transamination. Lactate can be converted back into pyruvate through the reverse reaction of LDH. Some organic acids and gluconeogenic intermediates can also enter the pyruvate node. Therefore, pyruvate is not only a glycolytic product but also an intersection point of carbon and nitrogen metabolism.

(3) Entry point for metabolic branching

Pyruvate can enter fermentation, the tricarboxylic acid cycle, gluconeogenesis, amino acid synthesis, lipid synthesis, and other pathways. PDC, LDH, and PDH are three representative branch enzymes corresponding to different metabolic strategies.

1.2 Basic Directions of the Three Branches

(1) PDC branch

In this article, PDC refers to pyruvate decarboxylase, not the “PDC” abbreviation used in some literature for the pyruvate dehydrogenase complex. PDC catalyzes the decarboxylation of pyruvate to acetaldehyde and CO₂ and is a key step in yeast ethanol fermentation.

(2) LDH branch

LDH, or lactate dehydrogenase, catalyzes the reaction between pyruvate and NADH to generate lactate and NAD⁺. Its core function is to maintain NAD⁺ regeneration required for glycolysis.

(3) PDH branch

PDH, or the pyruvate dehydrogenase complex, catalyzes oxidative decarboxylation of pyruvate to generate acetyl-CoA, CO₂, and NADH. It is the key entry point connecting glycolysis with the tricarboxylic acid cycle.

Table 1. Basic Functional Distinction Among PDC, LDH, and PDH

Enzyme	Chinese Name	Main Reaction	Metabolic Direction	Core Function
PDC	Pyruvate decarboxylase	Pyruvate → acetaldehyde + CO₂	First half of ethanol fermentation	Directs pyruvate toward ethanol production
LDH	Lactate dehydrogenase	Pyruvate + NADH ↔ lactate + NAD⁺	Lactate fermentation / lactate-pyruvate interconversion	Regenerates NAD⁺ and maintains glycolysis
PDH	Pyruvate dehydrogenase complex	Pyruvate + CoA + NAD⁺ → acetyl-CoA + CO₂ + NADH	Aerobic oxidative metabolism	Directs carbon flow into the TCA cycle and acetyl-CoA metabolism

2 PDC: Entry Point from Pyruvate to Ethanol Fermentation

2.1 Reaction Characteristics

(1) Catalytic reaction

PDC catalyzes the non-oxidative decarboxylation of pyruvate to produce acetaldehyde and carbon dioxide. This reaction does not directly generate NADH or directly consume NADH. Its function is to convert three-carbon pyruvate into two-carbon acetaldehyde.

(2) Cofactor requirements

PDC usually depends on thiamine pyrophosphate (TPP) and Mg²⁺. TPP stabilizes intermediates in the decarboxylation reaction and is a key cofactor for smooth pyruvate decarboxylation.

(3) Downstream reaction

The acetaldehyde generated by PDC is usually further reduced to ethanol by alcohol dehydrogenase (ADH), during which NADH is oxidized to NAD⁺. Therefore, PDC itself is not responsible for NAD⁺ regeneration, but together with ADH it forms the complete NADH reoxidation pathway in ethanol fermentation.

2.2 Metabolic Positioning

(1) Core step of ethanol fermentation

In yeast and other microorganisms, PDC is a hallmark enzyme of ethanol fermentation. Pyruvate generated by glycolysis enters the ethanol production pathway through PDC, allowing cells to continue obtaining ATP from glycolysis under oxygen-limited or high-glucose conditions.

(2) Carbon-flow discharge function

The PDC branch releases carbon flow as CO₂ and ethanol. For yeast, this helps rapidly consume sugar and maintain redox balance. However, in biomanufacturing, if the target product is not ethanol, the PDC branch may become a competing by-product pathway.

(3) Relationship with the Crabtree effect

Saccharomyces cerevisiae can favor ethanol fermentation under high-glucose conditions even when oxygen is present. PDC plays an important role in this fermentative metabolism and determines the strength of pyruvate diversion toward acetaldehyde and ethanol.

2.3 Engineering Significance

(1) Ethanol production

Increasing PDC and ADH flux can enhance ethanol fermentation capacity. In traditional brewing and fuel ethanol production, the PDC branch is the core carbon-flow route.

(2) Reduction of ethanol by-products

When producing organic acids, terpenoids, amino acids, or acetyl-CoA derivatives, PDC competes for pyruvate and carbon sources. Weakening PDC activity can reduce ethanol by-products, but NADH reoxidation and cell growth must be addressed simultaneously.

(3) Control of acetaldehyde toxicity

Acetaldehyde is reactive and cytotoxic. If PDC activity is enhanced while ADH activity or downstream reducing capacity is insufficient, acetaldehyde may accumulate, affecting cell viability and fermentation stability.

3 LDH: The Redox Valve Between Pyruvate and Lactate

3.1 Reaction Characteristics

(1) Reversible reaction

LDH catalyzes the reversible conversion between pyruvate and lactate. In the forward reaction, pyruvate accepts electrons from NADH to generate lactate, while NADH is oxidized to NAD⁺. In the reverse reaction, lactate can be oxidized to pyruvate and generate NADH.

(2) Redox balance function

The most important function of LDH is to maintain the cytosolic NADH/NAD⁺ balance. The glyceraldehyde-3-phosphate dehydrogenase step in glycolysis requires NAD⁺. If NAD⁺ is insufficient, glycolysis cannot continue. LDH oxidizes NADH back to NAD⁺, ensuring continued glycolytic operation.

(3) No CO₂ release

The LDH branch does not involve decarboxylation. Three-carbon pyruvate is reduced to three-carbon lactate, and the carbon number remains unchanged. This distinguishes LDH from PDC and PDH, both of which release CO₂.

3.2 Metabolic Positioning

(1) Hypoxia or high-glycolysis state

In animal cells, when hypoxia, insufficient mitochondrial oxidative capacity, or high glycolytic flux occurs, the LDH branch is enhanced and lactate generation increases. Intense skeletal muscle exercise, aerobic glycolysis in tumor cells, and activation of certain immune cells can all show increased LDH flux.

(2) Lactate shuttle

Lactate is not merely a metabolic waste product. It can be transported between different cells or tissues and reconverted into pyruvate in cells with stronger oxidative capacity, then enter PDH and the TCA cycle. Therefore, LDH participates in the lactate-pyruvate cycle and inter-tissue energy transfer.

(3) Fermentative metabolic outlet

In lactic acid bacteria and engineered yeast, LDH can direct pyruvate toward lactate production. Heterologous expression of LDH combined with weakening of the ethanol branch is a common strategy for constructing lactate-producing strains.

3.3 Isoenzyme Differences

(1) LDHA tendency

LDHA is often associated with the reduction of pyruvate to lactate and is frequently studied in high glycolysis, hypoxia, and tumor metabolism. Its enhancement usually suggests increased lactate production capacity.

(2) LDHB tendency

In some tissues, LDHB tends to favor conversion of lactate to pyruvate, supporting lactate utilization and oxidative metabolism. The actual reaction direction still depends on substrate concentrations, the NADH/NAD⁺ ratio, and the cellular metabolic environment.

(3) Interpretation boundary

Increased LDH expression cannot simply be equated with increased lactate generation. The direction of the LDH reaction is determined jointly by intracellular substrate ratios and redox status. Lactate release, pyruvate level, NADH/NAD⁺ ratio, and mitochondrial function should be analyzed together.

4 PDH: Gateway from Pyruvate to Oxidative Metabolism and Acetyl-CoA Metabolism

4.1 Reaction Characteristics

(1) Oxidative decarboxylation reaction

PDH catalyzes oxidative decarboxylation of pyruvate to generate acetyl-CoA, CO₂, and NADH. This reaction converts three-carbon pyruvate into a two-carbon acetyl group and links it to coenzyme A, providing an acetyl source for the TCA cycle, lipid synthesis, and acetylation reactions.

(2) Multienzyme complex structure

PDH is not a single enzyme but a multienzyme complex mainly composed of E1 pyruvate dehydrogenase, E2 dihydrolipoyl transacetylase, and E3 dihydrolipoyl dehydrogenase. Its reaction depends on multiple cofactors, including TPP, lipoic acid, CoA, FAD, and NAD⁺.

(3) Irreversibility

Under physiological conditions, the PDH reaction is essentially irreversible. Therefore, it is a key committed step for pyruvate entry into oxidative metabolism. Once pyruvate is converted into acetyl-CoA by PDH, carbon flow usually enters the TCA cycle, lipid synthesis, or acetylation metabolism and cannot directly return to pyruvate.

4.2 Subcellular Localization

(1) Mitochondrial localization in eukaryotic cells

In animal cells and most eukaryotic cells, PDH is located in the mitochondrial matrix. Cytosolic pyruvate must enter mitochondria through the mitochondrial pyruvate carrier before it can be used by PDH.

(2) Coupling with the TCA cycle

Acetyl-CoA generated by PDH can condense with oxaloacetate and enter the TCA cycle, further producing NADH, FADH₂, and GTP/ATP, providing reducing equivalents for oxidative phosphorylation.

(3) Relationship with lipid synthesis

Acetyl-CoA is also a key precursor for fatty acid synthesis, cholesterol synthesis, and acetylation modifications. Although mitochondrial acetyl-CoA cannot directly cross the inner mitochondrial membrane, it can provide carbon sources for cytosolic lipid synthesis through mechanisms such as the citrate shuttle.

4.3 Regulatory Mechanisms

(1) Phosphorylation regulation

In animal cells, PDH activity is regulated by PDH kinase (PDK) and PDH phosphatase (PDP). PDK phosphorylates the PDH E1 subunit and inhibits PDH activity. PDP dephosphorylates PDH and restores its activity.

(2) Energy status regulation

High NADH, high acetyl-CoA, and high ATP usually inhibit PDH, indicating sufficient cellular oxidative energy supply. High ADP, high pyruvate, and high Ca²⁺ favor PDH activation, indicating a cellular need to enhance oxidative metabolism.

(3) Pathology and metabolic adaptation

In hypoxia, tumor metabolism, inflammation, and certain metabolic diseases, PDK upregulation can inhibit PDH, causing pyruvate to preferentially generate lactate through LDH. Conversely, enhancing PDH flux can promote pyruvate entry into mitochondrial oxidative metabolism.

5 Core Differences Among PDC, LDH, and PDH

5.1 Differences in Carbon-Flow Direction

(1) PDC directs carbon flow toward the ethanol branch

PDC decarboxylates pyruvate into acetaldehyde, which is later converted to ethanol by ADH. This pathway typically exists in yeast ethanol fermentation and serves as an important outlet for carbon flow toward ethanol.

(2) LDH directs carbon flow toward the lactate branch

LDH reduces pyruvate to lactate while retaining the three-carbon skeleton. This pathway mainly serves NAD⁺ regeneration and lactate generation.

(3) PDH directs carbon flow toward the acetyl-CoA branch

PDH converts pyruvate into acetyl-CoA, connecting it to the TCA cycle, lipid synthesis, and acetylation metabolism. It is an important entry point for oxidative metabolism and biosynthesis.

5.2 Differences in NADH/NAD⁺ Relationship

(1) PDC does not directly consume NADH

PDC itself does not consume NADH, but its product acetaldehyde is reduced to ethanol by ADH, during which NADH is consumed and NAD⁺ is regenerated.

(2) LDH directly consumes NADH

When LDH generates lactate in the forward direction, it directly consumes NADH and generates NAD⁺. It is a key reaction for rapid regulation of cytosolic redox balance.

(3) PDH generates NADH

PDH reduces NAD⁺ to NADH, increasing the supply of mitochondrial reducing equivalents. This NADH can subsequently enter the respiratory chain for oxidative phosphorylation.

5.3 Differences in Energy Yield

(1) PDC and LDH maintain glycolytic ATP

PDC-ADH ethanol fermentation and LDH lactate fermentation do not themselves produce large amounts of additional ATP. Their main significance is regenerating NAD⁺ so that glycolysis can continue to generate a small amount of ATP.

(2) PDH supports high-energy oxidative metabolism

PDH allows pyruvate to enter the TCA cycle and oxidative phosphorylation. The overall ATP yield is much higher than that of simple fermentation pathways. This branch is suitable for conditions with sufficient oxygen supply and intact mitochondrial function.

(3) Different metabolic strategies

Fermentation branches emphasize rapid NAD⁺ regeneration and short-term glycolytic flux, whereas the PDH branch emphasizes complete oxidation of carbon sources, energy efficiency, and supply of biosynthetic precursors.

Table 2. Comparison of Metabolic Functions of PDC, LDH, and PDH

Comparison Dimension	PDC	LDH	PDH
Direct substrates	Pyruvate	Pyruvate/NADH or lactate/NAD⁺	Pyruvate, CoA, NAD⁺
Direct products	Acetaldehyde, CO₂	Lactate, NAD⁺	Acetyl-CoA, CO₂, NADH
Decarboxylation	Yes	No	Yes
Directly consumes NADH	No	Yes	No
Generates NADH	No	In reverse direction	Yes
Main significance	Entry point of ethanol fermentation	Cytosolic NAD⁺ regeneration	Entry point of oxidative metabolism
Typical scenarios	Yeast fermentation, high-glucose conditions	Hypoxia, high glycolysis, lactate generation	Aerobic metabolism, TCA cycle, lipid synthesis
Product risks	Acetaldehyde toxicity, ethanol by-products	Lactate accumulation, acidification	ROS pressure, mitochondrial burden

6 Branch Characteristics in Different Biological Systems

6.1 Yeast Systems

(1) Dominant PDC activity

In Saccharomyces cerevisiae, PDC is the core entry point for ethanol fermentation. Under high-glucose conditions, large amounts of pyruvate enter the PDC-ADH pathway to generate ethanol and regenerate NAD⁺.

(2) LDH mainly used in engineering modification

Most Saccharomyces cerevisiae strains do not naturally have strong lactate-producing capacity. If lactate production is the target, heterologous LDH is often introduced, and the ethanol branch is weakened so that more pyruvate enters the lactate pathway.

(3) PDH related to respiratory metabolism

Mitochondrial PDH in yeast participates in acetyl-CoA generation and respiratory metabolism. However, under high-glucose fermentation conditions, the PDC branch often dominates carbon flow.

6.2 Animal Cell Systems

(1) LDH related to hypoxic response

When animal cells experience hypoxia or reduced mitochondrial oxidative capacity, pyruvate tends to generate lactate through LDH to maintain glycolytic flux.

(2) PDH as the mitochondrial oxidative entry point

When oxygen supply is sufficient, pyruvate generates acetyl-CoA through PDH and enters the TCA cycle. Reduced PDH activity often causes pyruvate accumulation and diversion toward lactate production.

(3) PDC is usually not a major branch in animal cells

Typical animal cells do not use PDC-ethanol fermentation as a major pyruvate metabolic pathway. Therefore, in animal cell metabolic analysis, PDC is usually not discussed as a major pyruvate branch.

6.3 Bacterial and Engineered Microbial Systems

(1) Strong branch flexibility

Different bacteria may have multiple pyruvate branches, including lactate, ethanol, acetate, formate, and succinate. PDC, LDH, and PDH represent only part of the pyruvate metabolic network.

(2) High engineering value

Enhancing LDH-, PDC-, or PDH-related pathways can enable targeted production of lactate, ethanol, acetyl-CoA derivatives, or organic acids.

(3) Redox balance is critical

In microbial fermentation engineering, pyruvate branch selection must be designed together with NADH reoxidation, ATP generation, and by-product control. Simply enhancing one enzyme is often insufficient to stably increase yield.

7 Experimental Detection and Result Interpretation

7.1 Metabolite Detection

(1) Pyruvate

Increased pyruvate levels may indicate limitation of downstream branches, but may also reflect enhanced glycolytic flux. Lactate, ethanol, acetyl-CoA, and TCA intermediates should be analyzed together.

(2) Lactate

Increased lactate usually suggests enhanced forward LDH flux, but it is necessary to determine whether this results from increased production, enhanced export, or reduced utilization.

(3) Ethanol and acetaldehyde

Increased ethanol suggests enhancement of the PDC-ADH branch. Acetaldehyde accumulation may indicate strong PDC activity but insufficient ADH reduction capacity or mismatched NADH supply.

(4) Acetyl-CoA and TCA intermediates

Acetyl-CoA, citrate, α-ketoglutarate, malate, and other indicators can help determine changes in PDH and TCA cycle flux.

7.2 Enzyme Activity and Protein Detection

(1) PDC activity

PDC activity detection can be used to determine the entry capacity of ethanol fermentation and is often analyzed together with ethanol generation, CO₂ release, and ADH activity.

(2) LDH activity

LDH activity reflects lactate-pyruvate interconversion capacity, but cannot alone determine reaction direction. Lactate/pyruvate ratio and NADH/NAD⁺ status should be included.

(3) PDH activity

PDH activity is commonly evaluated through enzyme activity assays, PDH phosphorylation level, PDK/PDP expression, and mitochondrial respiration indicators. Increased PDH phosphorylation usually suggests PDH inhibition.

7.3 Isotope Tracing

(1) Carbon-flow tracing

¹³C-glucose or ¹³C-pyruvate can be used to trace the proportion of carbon flow entering lactate, ethanol, acetyl-CoA, and the TCA cycle.

(2) Branch quantification

Isotope labeling can distinguish changes in metabolite concentration from actual flux changes. For example, increased lactate concentration does not necessarily mean sustained enhancement of LDH flux; it may also be related to lactate export or decreased reutilization.

(3) Engineering evaluation

In metabolic engineering, isotope tracing helps determine whether PDC, LDH, or PDH modification truly changes carbon-flow distribution.

Table 3. Experimental Interpretation Indicators for Pyruvate Branches

Detection Indicator	Mainly Reflects	Associated Branch	Interpretation Notes
Lactate	Pyruvate reduction and NADH reoxidation	LDH	Should be interpreted with lactate export and NADH/NAD⁺
Ethanol	Reduced product of acetaldehyde	PDC-ADH	Should be interpreted with acetaldehyde and ADH activity
Acetaldehyde	Direct product of PDC	PDC	Volatile and toxic; detection requires rapid stabilization
Acetyl-CoA	PDH product and biosynthetic precursor	PDH	Affected by lipid synthesis and TCA consumption
NADH/NAD⁺	Redox status	LDH, PDH, ADH	Determines fermentation branch direction
PDH phosphorylation	PDH inhibition status	PDH	Increased phosphorylation usually indicates decreased PDH activity
OCR/ECAR	Respiration and glycolytic status	LDH/PDH	Should be combined with direct metabolite detection

8 Common Misunderstandings and Key Distinctions

8.1 Confusing PDC with PDH

PDC can have two meanings in different literature contexts: pyruvate decarboxylase or pyruvate dehydrogenase complex. When discussing PDC, LDH, and PDH together, it should be clearly stated that PDC refers to pyruvate decarboxylase and PDH refers to pyruvate dehydrogenase complex to avoid abbreviation confusion.

8.2 Equating Lactate Generation with Hypoxia

Lactate generation is common in hypoxia but does not occur only under hypoxic conditions. High glycolysis, restricted mitochondrial function, tumor metabolic reprogramming, and immune cell activation can all enhance lactate production. LDH flux should be evaluated together with oxygen consumption, mitochondrial function, and glycolytic flux.

8.3 Equating Decreased PDH Activity with Complete Mitochondrial Inactivation

Reduced PDH activity limits pyruvate entry into the TCA cycle, but mitochondria may still use fatty acids, glutamine, or other substrates to maintain partial oxidative metabolism. Mitochondrial status should be assessed using OCR, membrane potential, TCA metabolites, and respiratory-chain function.

8.4 Ignoring Redox Balance

The shared value of the PDC-ADH and LDH branches lies in NAD⁺ regeneration, whereas PDH generates NADH and depends on mitochondrial oxidative capacity. If only carbon flow is considered without NADH/NAD⁺, the real cause of branch changes can be misinterpreted.

Table 4. Quick Logic for Distinguishing PDC, LDH, and PDH

Interpretation Question	Priority Branch	Key Judgment
Is ethanol fermentation occurring?	PDC-ADH	Ethanol, acetaldehyde, and CO₂ release increase
Is lactate generation enhanced?	LDH	Lactate increases and NAD⁺ regeneration demand rises
Is pyruvate entering the TCA cycle?	PDH	Acetyl-CoA and TCA intermediates increase
Is glycolytic NAD⁺ maintained?	LDH or PDC-ADH	NADH is oxidized back to NAD⁺
Is oxidative decarboxylation occurring?	PDH	Acetyl-CoA and NADH are generated
Is non-oxidative decarboxylation occurring?	PDC	Acetaldehyde and CO₂ are generated
Is the three-carbon skeleton retained?	LDH	Pyruvate and lactate interconvert

9 Product Selection for PDC, LDH, and PDH Branch Research

Table 5. Core Detection Products for PDC, LDH, and PDH Branch Research

Product Category	Cat. No.	Product Name	Grade / Specification	Role in the System	Applicable Direction
Pyruvate node detection	P1515881	Pyruvic Acid (PA) Content Assay Kit (LDH, Micro Method)	BioReagent	Detects pyruvate content based on an LDH-coupled system	Pyruvate node quantification; LDH/PDH/PDC branch research
Pyruvate node detection	P1515904	Pyruvic Acid (PA) Content Assay Kit (LDH, Colorimetric Method)	BioReagent	Performs pyruvate colorimetric detection through an LDH-coupled reaction	Pyruvate quantification in cells, tissues, or fermentation samples
Pyruvate node detection	P1515903	Pyruvic Acid (PA) Content Assay Kit (DNPH, Colorimetric Method)	BioReagent	Detects pyruvate through a DNPH chromogenic system	Pyruvate accumulation, downstream branch limitation, and flux analysis
PDC sample processing	P1518228	Pyruvate decarboxylase (PDC) extraction reagent	BioReagent,Suitable for plant cell and tissue extracts	Extracts PDC-related enzyme components from samples	Pretreatment before PDC activity detection, suitable for plant samples
PDC activity detection	P1521907	Pyruvate Decarboxylase (PDC) Activity Assay Kit (UV Micro Method)	BioReagent	Detects the ability of PDC to catalyze pyruvate decarboxylation and acetaldehyde generation	Ethanol fermentation branch; yeast/plant PDC flux analysis
PDC activity detection	P1521908	Pyruvate Decarboxylase (PDC) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Evaluates PDC activity by colorimetry	PDC-ADH ethanol fermentation pathway; hypoxic fermentation research
PDH activity detection	P1515804	Pyruvate Dehydrogenase (PDH) Activity Assay Kit (DCPIP, Micro Method)	BioReagent	Detects PDH oxidative decarboxylation activity and reflects pyruvate entry into the acetyl-CoA branch	PDH flux, TCA entry, mitochondrial oxidative metabolism research
ADH sample processing	E1518221	Ethanol Dehydrogenase (ADH) Extraction Reagent	BioReagent,Suitable for plant cell and tissue extracts	Extracts ADH-related enzyme components from samples	Pretreatment before downstream ADH activity detection in the PDC branch
ADH activity detection	A1515884	Alcohol Dehydrogenase (ADH) Activity Assay Kit (UV Micro Method)	BioReagent	Detects acetaldehyde-ethanol interconversion capacity	PDC-ADH branch integrity and acetaldehyde reduction capacity evaluation
ADH activity detection	A1515885	Alcohol Dehydrogenase (ADH) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects ADH activity by colorimetry	Ethanol metabolism, acetaldehyde reduction, and fermentation flux analysis
Ethanol branch product detection	E1515848	Ethanol Content Detection Kit (WST-8, Micro Method)	BioReagent	Quantitatively detects ethanol content	Evaluation of the PDC-ADH ethanol fermentation branch
Ethanol branch product detection	E1515967	Ethanol Content Assay Kit (WST-8, Colorimetric Method)	BioReagent	Detects ethanol content by colorimetry	Ethanol generation, PDC branch strength, and fermentation end-product analysis
Core LDH activity detection	D1373349	L-Lactate Dehydrogenase Assay Kit (WST-8)	BioReagent,Colorimetry,Suitable for Analysis	Detects L-LDH-related activity	L-lactate generation, enhanced glycolysis, and LDH branch evaluation
Core LDH activity detection	L1510342	Lactate Dehydrogenase (LDH) Activity Assay Kit (LD-L, Colorimetric Method)	BioReagent	Detects LDH-catalyzed lactate-pyruvate interconversion capacity	LDH branch activity and lactate generation capacity analysis
Core LDH activity detection	L1521751	Lactate Dehydrogenase (LDH) Activity Assay Kit (LD-P, UV Colorimetric Method)	BioReagent	Detects LDH activity by UV colorimetry	Lactate/pyruvate redox balance analysis
D-LDH activity detection	D1505517	D-Lactate Dehydrogenase (D-LDH) Activity Assay Kit (DNPH, Micro Method)	BioReagent	Detects D-LDH-related activity	Microbial D-lactate fermentation and D/L-lactate branch distinction
L-lactate detection	L486214	L-Lactate Assay Kit	Colorimetry, 100 assays(96 samples)	Detects L-lactate content	LDH forward flux, lactate export, and glycolytic level analysis
L-lactate detection	L1373335	L-Lactate Assay Kit (WST-8)	BioReagent,Colorimetry,Suitable for Analysis	Quantifies L-lactate with a WST-8 system	Lactate quantification in cell culture supernatants, fermentation broth, or tissue samples
D-lactate detection	D1501940	D-Lactic acid (D-LA) Content Assay Kit (WST-8, Micro Method)	BioReagent	Detects D-lactate content	Microbial fermentation and D/L-lactate isomer distinction
D-lactate detection	D486223	D-Lactate Colorimetric Assay	sufficient for 100colorimetrictests	Detects D-lactate by colorimetry	D-lactate-producing strains and lactate fermentation product analysis
LDH cytotoxicity detection	L1501786	Lactate Dehydrogenase (LDH) Cytotoxicity Assay Kit (DNPH, Micro Method)	BioReagent	Detects extracellular LDH release using a DNPH system	Cell membrane integrity and safety evaluation of metabolic interventions
LDH cytotoxicity detection	L1373310	LDH Cytotoxicity Assay Kit with WST-8	BioReagent,ready-to-use,for IP	Ready-to-use LDH release detection system	Evaluation of drug treatment, metabolic regulation, or cell injury models
LDH cytotoxicity detection	L1521750	Lactate Dehydrogenase (LDH) Cytotoxicity Assay Kit (DNPH, Colorimetric Method)	BioReagent	Evaluates extracellular LDH release by colorimetry	Cell toxicity, membrane injury, and safety analysis of metabolic inhibitors
Acetyl-CoA detection	A1515818	Acetyl Coenzyme A (Acetyl-CoA) Assay Kit (UV Micro Method)	BioReagent	Detects acetyl-CoA content and reflects changes in the PDH product pool	PDH branch, TCA entry, and lipid synthesis precursor analysis

Table 6. Enzymatic Materials Related to PDC, LDH, and PDH Branch Research

Product Category	Cat. No.	Product Name	Grade / Specification	Role in the System	Applicable Direction
PDC enzymatic material	P1374084	Pyruvate Decarboxylase (PDC)	Bioactive, Recombinant, ActiBioPure™, High Performance, EnzymoPure™, ≥1 U/mg enzyme powder; ≥5 U/mg protein	Catalyzes non-oxidative decarboxylation of pyruvate to acetaldehyde and CO₂	In vitro enzymatic validation of the PDC branch; yeast ethanol fermentation flux research
Pyruvate-related enzyme	P774057	Pyruvate oxidase	ActiBioPure™, EnzymoPure™, Bioactive, High Performance, ≥90%(SDS-PAGE), ≥50 U/mg protein	Catalyzes pyruvate oxidation and can be used in pyruvate-coupled detection systems	Pyruvate quantification, enzyme-coupled detection, and pyruvate node analysis
Terminal glycolytic enzyme	P774071	Pyruvate Kinase (PK)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥90%(SDS-PAGE),≥50 U/mg enzyme powder; ≥300 U/mg protein	Catalyzes PEP to pyruvate	Terminal glycolytic carbon supply and pyruvate generation rate analysis
Terminal glycolytic enzyme	P1510309	Pyruvate Kinase (PK)	Bioactive,ActiBioPure™,Native,High Performance,EnzymoPure™,from Rabbit muscle; ≥200 U/mg enzyme powder	Catalyzes PEP conversion to pyruvate	In vitro enzymology and upstream glycolytic carbon-supply evaluation
Competing pyruvate branch enzyme	P1431075	Pyruvate carboxylase		Catalyzes pyruvate carboxylation to oxaloacetate	Pyruvate anaplerosis, competing branch with PDH, and TCA replenishment analysis
ADH enzymatic material	R1442285	(R)-Alcohol dehydrogenase		Catalyzes redox conversion of alcohol/aldehyde-ketone substrates	ADH-coupled reactions, alcohol metabolism, and chiral substrate conversion research
ADH enzymatic material	A124756	Alcohol Dehydrogenase from Saccharomyces cerevisiae	Bioactive,ActiBioPure™,High Performance,EnzymoPure™,Native,≥300 units/mg protein	Catalyzes acetaldehyde-ethanol interconversion	PDC-ADH ethanol fermentation pathway and acetaldehyde reduction capacity analysis
ADH enzymatic material	rp226533	Recombinant Alcohol Dehydrogenase (ADH)	Bioactive, ActiBioPure™, High Performance, EnzymoPure™, ≥90%(SDS-PAGE), ≥100 U/mg protein	Recombinant ADH enzymatic reaction material	ADH activity validation and ethanol/acetaldehyde interconversion analysis
LDH enzymatic material	R1506878	D-Lactate Dehydrogenase (LDHD)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥220 U/mg enzyme powder	Participates in D-lactate-related redox conversion	Microbial D-lactate metabolism and D/L-lactate branch distinction
LDH enzymatic material	L139685	Lactate Dehydrogenase from Staphylococcus sp.	EnzymoPure™, ＞100U/mg	Catalyzes lactate-pyruvate interconversion	Microbial LDH reactions and in vitro validation of the lactate branch
LDH enzymatic material	L1492991	Recombinant L-Lactate Dehydrogenase (L-LDH)	ActiBioPure™, Bioactive, High Performance, EnzymoPure™, Recombinant, >260 U/mg protein	Catalyzes reversible conversion between pyruvate and L-lactate	L-lactate generation, LDH branch, and NADH/NAD⁺ balance research
LDH enzymatic material	L196994	Recombinant L-Lactate Dehydrogenase (L-LDH)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥90%(SDS-PAGE),≥80 U/mg enzyme powder; ≥300 U/mg protein	High-activity L-LDH enzymatic material	Lactate generation systems and LDH-coupled detection
LDH enzymatic material	D649636	Recombinant Lactate Dehydrogenase (LDH)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥90%(SDS-PAGE),≥420U/mg enzyme powder	Catalyzes lactate-pyruvate interconversion	LDH activity research and lactate/pyruvate redox balance analysis
PEPC enzymatic material	P774064	Recombinant Phosphoenolpyruvate Carboxylase (PEPC)	ActiBioPure™, Bioactive, High Performance, EnzymoPure™, ≥80 U/mg protein	Catalyzes PEP carboxylation to oxaloacetate-related products	Adjacent PEP-pyruvate carbon flow; plant/microbial carbon metabolism research
MDH enzymatic material	R1506880	Malate Dehydrogenase (MDH)	Bioactive,ActiBioPure™,High Performance,EnzymoPure™,Recombinant,≥40 U/mg enzyme powder; expressed in E.coli	Catalyzes malate-oxaloacetate interconversion	PDH downstream TCA coupling, NADH readout, and mitochondrial metabolism analysis
MDH enzymatic material	M139683	Malate dehydrogenase (MDH) from Thermus sp.	Bioactive,ActiBioPure™,Native,High Performance,EnzymoPure™,≥100 U/mg enzyme powder	Thermostable-source MDH reaction material	TCA cycle coupling and in vitro enzyme-coupled systems
MDH enzymatic material	R1505812	Recombinant Malate Dehydrogenase (MDH)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥50U/mg enzyme powder; ≥200U/mg protein	Catalyzes malate-oxaloacetate interconversion	Evaluation of PDH downstream TCA status
MDH enzymatic material	M196993	Malate Dehydrogenase，recombinant from bacteria	EnzymoPure™, ＞ 550 units/mg	High-activity MDH enzymatic material	NADH readout systems and metabolic coupled reactions
GDH enzymatic material	L489276	L-Glutamic Dehydrogenase (NADP)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,>60 U/mg protein	NADP(H)-dependent glutamate metabolism reaction	NADPH/NADP⁺ status and carbon-nitrogen metabolic crosstalk research
GDH enzymatic material	R1507821	L-Glutamic Dehydrogenase (NADP)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥2000U/ml; ≥400U/mg protein	High-activity NADP-type GDH	Combined analysis of nitrogen metabolism and TCA cycle
GDH regulator	R304260	R162	≥98%	Inhibits GDH1-related activity	Mechanistic research on crosstalk between pyruvate and amino acid metabolism
GDH enzymatic material	G776693	Glutamate Dehydrogenase (GLDH)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥90%(SDS-PAGE),≥200 U/mg enzyme powder; ≥400 U/mg protein	Catalyzes glutamate-α-ketoglutarate interconversion	TCA-amino acid metabolism crosstalk and NAD(P)H status analysis
GDH enzymatic material	G1492998	Glutamate Dehydrogenase (NAD-GDH) from Microorganism	Bioactive,ActiBioPure™,Native,High Performance,EnzymoPure™,≥100 U/mg enzyme powder	NAD-dependent GDH reaction material	α-Ketoglutarate-related metabolism and carbon-nitrogen metabolic coupling
GDH enzymatic material	R1505822	Recombinant Glutamate Dehydrogenase (NAD-GDH)	Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥80 U/mg enzyme powder	Recombinant NAD-GDH enzymatic material	TCA coupling and amino acid metabolism crosstalk
Acetyl-CoA standard/substrate	A466839	Acetyl-Coenzyme A trilithium salt	85% (Enzymatic and Absorbance), 2% (lithium)	Used as an acetyl-CoA source or standard	PDH product pool, TCA entry, and lipid synthesis precursor analysis
Acetyl-CoA standard/substrate	A336151	Acetyl coenzyme A trilithium salt	≥85%	Acetyl-CoA substrate/standard	Acetyl-CoA-related enzymatic reaction systems
Acetyl-CoA standard/substrate	A463299	Acetyl coenzyme A sodium salt	≥90%	Acetyl-CoA source	PDH downstream metabolism and acetyl-CoA branch analysis

Table 7. Products for Adjacent Pyruvate Pathways, TCA Coupling, and Auxiliary Evaluation

Product Category	Cat. No.	Product Name	Grade / Specification	Role in the System	Applicable Direction
PK activity detection	A1501205	Pyruvate Kinase (PK) Activity Assay Kit (UV Micro Method)	BioReagent	Detects terminal glycolytic PK activity	Pyruvate generation rate and glycolytic carbon-supply analysis
PPDK activity detection	P1501938	Pyruvate Phosphate Dikinase (PPDK) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects PPDK activity	Plant/microbial PEP-pyruvate interconversion analysis
PPDK activity detection	P1501935	Pyruvate Phosphate Dikinase (PPDK) Activity Assay Kit (UV Micro Method)	BioReagent	Detects PPDK activity by micro method	Adjacent carbon-flow regulation around pyruvate
PC activity detection	P1515970	Pyruvate Carboxylase (PC) Activity Assay Kit (UV Micro Method)	BioReagent	Detects pyruvate carboxylation capacity to generate oxaloacetate	Pyruvate anaplerosis and competing branch analysis with PDH
PC activity detection	P1515971	Pyruvate Carboxylase (PC) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects PC activity by colorimetry	Pyruvate diversion, gluconeogenesis, or anaplerotic metabolism research
PEPC activity detection	P1515972	Phosphoenolpyruvate Carboxylase (PEPC) Activity Assay Kit (UV Micro Method)	BioReagent	Detects PEPC activity	PEP carboxylation, oxaloacetate replenishment, and plant carbon metabolism
PEPC activity detection	P1515973	Phosphoenolpyruvate Carboxylase (PEPC) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects PEPC activity by colorimetry	Plant/microbial carbon-flow replenishment reactions
PEPCK activity detection	P1501278	Phosphoenol Pyruvate Carboxykinase (PEPCK) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects PEPCK activity	Gluconeogenesis and oxaloacetate-PEP conversion analysis
PEPCK activity detection	P1501322	Phosphoenol Pyruvate Carboxykinase (PEPCK) Activity Assay Kit (UV Micro Method)	BioReagent	Detects PEPCK activity by micro method	PEP/pyruvate supply-demand relationship analysis
CS activity detection	C1515840	Citrate Synthase (CS) Activity Assay Kit (DTNB, Micro Method)	BioReagent	Detects the entry enzyme activity for acetyl-CoA entering the TCA cycle	PDH-TCA coupling and mitochondrial oxidative metabolism evaluation
NAD-MDH activity detection	N1515808	NAD-Malate Dehydrogenase（NAD-MDH）Activity Assay Kit (UV Micro Method)	BioReagent	Detects NAD-dependent MDH activity	TCA cycle, NADH status, and PDH downstream coupling analysis
NAD-MDH activity detection	N1515938	NAD-Malate Dehydrogenase (NAD-MDH) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects NAD-MDH activity by colorimetry	Mitochondrial/cytosolic malate metabolism analysis
NADP-MDH activity detection	N1515807	NADP-Malate Dehydrogenase（NADP-MDH）Activity Assay Kit (UV Micro Method)	BioReagent	Detects NADP-dependent MDH activity	NADPH-related reducing power analysis and carbon metabolism coupling
NADP-MDH activity detection	N1515937	NADP-Malate Dehydrogenase (NADP-MDH) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects NADP-MDH activity by colorimetry	NADP(H) balance and TCA bypass analysis
Mitochondrial MDH detection	M1515806	Mitochondrial Malate Dehydrogenase(mMDH) Activity Assay Kit (UV Micro Method)	BioReagent	Detects mitochondrial MDH activity	Evaluation of downstream mitochondrial oxidative metabolism after PDH
Mitochondrial MDH detection	M1515936	Mitochondrial Malate Dehydrogenase (mMDH) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects mMDH activity by colorimetry	Mitochondrial TCA cycle status analysis
MDH sample processing	A1518214	Malate Dehydrogenase (MDH) Extraction Reagent	BioReagent	Extracts MDH-related enzyme components from samples	Pretreatment before MDH activity detection
MDH activity detection	L1507463	Malate Dehydrogenase Activity Assay Kit (WST-8)	BioReagent,Colorimetry,Suitable for Analysis	Detects MDH activity using a WST-8 system	TCA coupling and malate-oxaloacetate conversion analysis
GDH activity detection	G1505936	Glutamic Dehydrogenase (GDH) Activity Assay Kit (UV Micro Method)	BioReagent	Detects GDH activity	α-Ketoglutarate-related metabolism and TCA-amino acid crosstalk analysis
GDH activity detection	G1515931	Glutamate Dehydrogenase (GDH) Activity Assay Kit (UV Colorimetric Method)	BioReagent	Detects GDH activity by colorimetry	Combined nitrogen and carbon metabolism analysis
ACC activity detection	A1515852	Acetyl CoA Carboxylase (ACC) Activity Assay Kit (AHM, Micro Method)	BioReagent	Detects activity related to conversion of acetyl-CoA toward fatty acid synthesis	Analysis of PDH-derived acetyl-CoA diversion into lipid synthesis
ACC activity detection	A1515969	Acetyl-CoA Carboxylase (ACC) Activity Assay Kit (AHM, Colorimetric Method)	BioReagent	Detects ACC activity by colorimetry	Evaluation of acetyl-CoA diversion into lipid synthesis
ATP detection	A1515819	ATP Content Assay Kit (AHM, Micro Method)	BioReagent	Detects ATP level	Comparison of energy yield between PDC/LDH fermentation branches and the PDH oxidative branch
Inorganic phosphate detection	I1510382	Inorganic Phosphate Content Assay Kit (UV Micro Method)	BioReagent	Detects inorganic phosphate and supports evaluation of energy metabolism background	Combined analysis of ATP metabolism, glycolysis, and oxidative phosphorylation
Inorganic phosphate detection	I1510435	Inorganic Phosphate Content Assay Kit (UV Colorimetric Method)	BioReagent	Detects inorganic phosphate by colorimetry	Auxiliary indicator analysis of energy metabolism
Cell viability detection	C266180	Cell Counting Kit-8	BioReagent,for detection	Evaluates cellular metabolic activity	Cell status analysis after LDH inhibition, PDH activation, or pyruvate supplementation
Cell viability detection	S707171	Solid instant dissolution Cell Counting Kit-8		Evaluates cell proliferation and metabolic activity	Cell viability detection after branch regulation treatments
Cell viability detection	C1375225	MTT Cell Proliferation and Cytotoxicity Assay Kit	BioReagent	Detects cell metabolic activity and toxicity response	Evaluation of cell injury and viability after PDC, LDH, or PDH regulation

PDC, LDH, and PDH represent different directions of pyruvate metabolism in fermentation, redox balance, and oxidative metabolism. PDC directs carbon flow toward ethanol fermentation, LDH maintains the NADH/NAD⁺ balance between pyruvate and lactate, and PDH connects pyruvate to acetyl-CoA and the TCA cycle. Accurately distinguishing these three enzymes helps clarify carbon-flow allocation in hypoxia, high-glucose metabolism, fermentation, tumor metabolism, and metabolic engineering contexts.

For more related articles, please see below:

[1] Determination of phosphoenolpyruvate carboxylase activity