Progress in Research on the S-Adenosylmethionine Cycle and Regulatory Mechanisms of Methyltransfer Reactions

S-Adenosylmethionine is one of the most important activated methyl donors in cells and is widely involved in methyl-transfer reactions affecting DNA, RNA, proteins, lipids, and multiple classes of small molecules. Current understanding of methylation regulation has expanded from the level of "methyl-donor supply" to an integrated network level encompassing donor formation, product clearance, cyclic regeneration, branch competition, and signaling-based sensing. The S-adenosylmethionine cycle not only determines methyl-donor availability, but also systematically affects the rate, direction, and output spectrum of methyl-transfer reactions through mechanisms such as S-adenosylhomocysteine accumulation, allocation of homocysteine fate, remethylation efficiency, and methyl-sink formation. Therefore, the S-adenosylmethionine cycle should be regarded as the core metabolic control layer of methyl-transfer homeostasis, rather than merely a background system for donor supply.

 

Keywords: S-adenosylmethionine; SAM cycle; methyl-transfer reactions; S-adenosylhomocysteine; one-carbon metabolism; methionine cycle; methyl donor; epigenetic regulation

 

1. Metabolic Positioning of the S-Adenosylmethionine Cycle

1.1 Composition of the cycle and its metabolic connections

(1) Basic composition of the SAM cycle

The S-adenosylmethionine cycle generally consists of methionine activation, methyl transfer, clearance of S-adenosylhomocysteine, remethylation of homocysteine, and diversion into the transsulfuration pathway. Methionine is conjugated with ATP under the action of methionine adenosyltransferase to generate S-adenosylmethionine. The latter transfers its methyl group to acceptor molecules under the catalysis of multiple classes of methyltransferases, thereby forming S-adenosylhomocysteine. S-Adenosylhomocysteine is then converted by adenosylhomocysteinase into homocysteine. Homocysteine can subsequently regenerate methionine through folate-dependent or betaine-dependent pathways, thereby completing closure of the cycle. This process is tightly coupled to the folate cycle, one-carbon-unit supply, and sulfur-containing metabolic networks.

(2) Coupling between methyl-donor metabolism and the nutritional background

Methionine, folate, choline/betaine, and serine-glycine metabolism jointly participate in one-carbon-unit supply and homocysteine remethylation. Accordingly, the SAM cycle is intrinsically constrained by nutritional status and the availability of metabolic substrates. It follows that changes in methylation capacity do not usually arise from altered expression of a single methyltransferase, but rather reflect the combined effects of substrate supply, cyclic regeneration, cofactor support, and branch competition.

 

1.2 Regulatory significance of the SAM cycle in methylation reactions

(1) Broad donor properties of SAM

S-Adenosylmethionine is one of the most widely used methyl donors in cells and can be utilized by large numbers of DNA, RNA, protein, and small-molecule methyltransferases. As a result, changes in SAM levels and turnover status exert pronounced systemic effects, often influencing multiple layers of methylation output simultaneously rather than remaining confined to a single modification system.

(2) Methylation potential is determined by the state of the cycle

Current research increasingly emphasizes that "methylation potential" is a composite state jointly defined by donor formation and product clearance, and should not be simplified to the concentration of SAM alone. Even when SAM is relatively abundant, methyl-transfer reactions may still be markedly inhibited if SAH accumulates simultaneously. Conversely, under conditions of efficient SAH clearance, even moderate SAM levels may support relatively strong methylation output. Therefore, the SAM/SAH ratio has greater mechanistic interpretive value than measurement of SAM alone.

 

2. Key Metabolic Nodes in the S-Adenosylmethionine Cycle

2.1 The SAM-generation node

(1) Entry-point role of methionine adenosyltransferase

Methionine adenosyltransferase catalyzes the formation of S-adenosylmethionine from methionine and ATP and is the direct entry point for activated methyl-donor formation. This step determines whether the methylation system obtains a sufficient supply of activated methyl donor, and it also represents the most direct metabolic interface linking nutritional input and methionine availability to downstream methyl-transfer reactions.

(2) Regulatory significance of the MAT node

In multicellular eukaryotic systems, MAT is not a constitutively fixed-output enzyme, but is regulated jointly by transcription, splicing, and metabolic state. Particularly in most non-hepatic cells, MAT2A is the principal SAM synthase. Its expression level, mRNA-processing status, and protein stability directly determine the capacity for intracellular SAM supply, and further influence the global background of methylation reactions.

 

2.2 Methyl-transfer reaction nodes

(1) Shared metabolic features of methyl-transfer reactions

Whether the relevant enzymes are DNA methyltransferases, RNA methyltransferases, lysine/arginine methyltransferases, or small-molecule methyltransferases such as glycine N-methyltransferase and nicotinamide N-methyltransferase, they share a common metabolic feature: consumption of SAM and generation of SAH. Thus, although different methylation systems act on different substrates, they share the same donor pool and the same product-inhibition pressure at the metabolic level.

(2) Diversity of acceptors and complexity of regulation

Methyl acceptors include nucleic acids, histones, non-histone proteins, membrane lipids, and multiple classes of metabolites. This determines that regulation of methyl-transfer reactions by the SAM cycle has broad-spectrum and hierarchically propagated effects. When SAM supply is insufficient or SAH accumulates, the affected outputs extend beyond epigenetic modifications to include RNA fate control, signal transduction, membrane-lipid metabolism, and metabolite clearance.

 

2.3 SAH clearance and reutilization of homocysteine

(1) Central role of SAHH/AHCY

S-Adenosylhomocysteine hydrolase is the key enzyme responsible for SAH clearance and is also the core node for direct SAH degradation in most eukaryotic cells. Because SAH exerts strong inhibitory effects on multiple classes of methyltransferases, the function of SAHH is not simply "metabolic clearance," but rather a prerequisite for maintaining continuity of methyl-transfer reactions.

(2) Remethylation and transsulfuration diversion

Homocysteine produced after SAH hydrolysis can either regenerate methionine through folate-dependent or betaine-dependent pathways, or enter the transsulfuration pathway to generate cysteine and downstream sulfur-containing metabolites. Accordingly, the SAM cycle is not a closed loop, but rather an open network in which homocysteine is continuously allocated between donor regeneration and sulfur-metabolism output.

Table 1. Key nodes in the S-adenosylmethionine cycle and their regulatory significance

 

Metabolic Node	Core Intermediate	Major Enzyme/Module	Position in the Cycle	Major Regulatory Significance
Methyl-donor formation	Methionine, ATP, SAM	MAT1A/MAT2A	Cycle entry	Determines the capacity for activated methyl-donor formation
Methyl-transfer output	SAM, SAH	DNA/RNA/protein/small-molecule methyltransferases	Core consumption layer of the cycle	Determines the specific output direction of methyl-transfer reactions
Product clearance	SAH	SAHH/AHCY	Feedback-relief layer	Removes product inhibition and maintains continuity of methylation
Homocysteine remethylation	Homocysteine, methionine	Folate-dependent/betaine-dependent remethylation systems	Cycle-regeneration layer	Maintains regeneration of methionine and the SAM donor pool
Transsulfuration diversion	Homocysteine, cysteine	CBS, CTH, etc.	Bypass of the cycle	Determines the balance between methyl-unit reutilization and sulfur-metabolism output

 

3. Major Output Layers of Methyl-Transfer Reactions

3.1 Nucleic-acid methylation

(1) DNA methylation

DNA methylation is one of the most classical SAM-dependent methyl-transfer outputs. DNA methyltransferases use SAM as the methyl donor to generate methylated cytosine while simultaneously producing SAH. Because maintenance of DNA methylation after replication depends on sustained activity of enzymes such as DNMT1, DNA methylation is particularly sensitive to the efficiency of SAH clearance.

(2) RNA methylation

RNA methylation likewise represents an important SAM-dependent output layer. RNA modification systems represented by m6A not only consume SAM, but their key regulatory factors may also participate in sensing cellular SAM homeostasis and in feedback regulation, thereby coupling donor-metabolic status to RNA-processing fate.

 

3.2 Protein methylation

(1) Histone methylation

Methylation of histone lysine and arginine residues is a key interface linking metabolic status to chromatin structure. Methionine supply and changes in SAM/SAH can drive alterations in specific histone methylation marks and further influence transcriptional programs. Accordingly, histone methylation is not only an epigenetic terminal readout, but also a functional output layer of metabolic status.

(2) Non-histone protein methylation

In addition to histones, multiple transcription factors, signaling proteins, and metabolic enzymes can also undergo methylation. This extends the regulatory effects of the SAM cycle beyond the chromatin layer to signal transduction, protein stability, and remodeling of enzyme activity. Consequently, alterations in methyl-donor homeostasis often produce broad functional spillover effects.

 

3.3 Methylation of small molecules and metabolites

(1) Metabolic buffering and methyl-sink function

Small-molecule methyltransferases are not only branch enzymes of metabolism, but can also function as methyl sinks. Typical examples include GNMT and NNMT, which can indirectly influence DNA, RNA, and histone methylation by continuously consuming SAM and thereby altering the cellular methyl-donor pool. GNMT is commonly regarded as a methyl-donor buffering node, whereas increased NNMT is often accompanied by a reduced SAM/SAH ratio and remodeling of epigenetic modifications.

(2) System-level significance of metabolite methylation

Such methyl-sink mechanisms indicate that different methyl-transfer reactions are not independent of one another. Enhancement of a given small-molecule methylation branch may competitively consume SAM or increase SAH burden, thereby further affecting broader nucleic-acid and protein methylation outputs.

 

4. Regulatory Mechanisms Linking the SAM Cycle to Methyl-Transfer Reactions

4.1 Regulation by substrate supply

(1) Supply of methionine and one-carbon units

Methyl-transfer capacity is first constrained by methionine supply, one-carbon-unit generation, and remethylation efficiency. Methionine limitation can reduce SAM levels and affect nucleic-acid and histone methylation, whereas the folate cycle and betaine pathway determine whether homocysteine can efficiently return to the methionine pool. Therefore, regulation of methylation is intrinsically highly nutrient-dependent.

(2) Regulation of MAT2A expression and splicing

In most cells, MAT2A is the principal synthase maintaining SAM supply. Relevant RNA-processing factors can regulate the retained-intron splicing status of MAT2A, thereby affecting MAT2A mRNA abundance and intracellular SAM homeostasis. This indicates that SAM supply is constrained not only by substrate availability, but also by post-transcriptional processing control.

 

4.2 Product-feedback inhibition

(1) Broad inhibitory effects of SAH

SAH is a potent inhibitory product for multiple classes of methyltransferases. Therefore, in many contexts, the main limitation on methyl-transfer reactions is not absolute insufficiency of SAM, but rather feedback inhibition caused by delayed SAH clearance. Changes in SAHH activity can rapidly alter the operating state of multiple methylation systems.

(2) Interpretive advantage of the SAM/SAH ratio

Compared with measurement of SAM alone, the SAM/SAH ratio better reflects the true driving force of the methyl-transfer system. A decline in this ratio generally indicates reduced methylation potential. Even when SAM itself has not decreased markedly, downstream methyl-transfer reactions may still become limited because of elevated SAH.

 

4.3 Metabolic sensing and signal integration

(1) Sensing function of SAMTOR

SAM is not only a metabolic substrate but can also be sensed as a signaling molecule. SAMTOR is considered an important SAM-sensing protein. When bound to SAM, it can regulate the functional state of upstream nutrient-signaling complexes, thereby translating methionine/SAM supply status into growth- and metabolism-related signaling outputs.

(2) Expansion from metabolic homeostasis to growth homeostasis

This mechanism indicates that the regulatory significance of the SAM cycle is not limited to methylation itself. Changes in SAM levels can also influence nutrient response, cell growth, and signal transduction through metabolic-sensing proteins. Thus, methyl-donor metabolism has become an important component of the cellular network for sensing overall physiological state.

 

4.4 Methyl-sink and buffering mechanisms

(1) Buffering role of GNMT

GNMT is widely regarded as an important buffering enzyme that regulates SAM levels and the SAM/SAH ratio. Increased GNMT can increase methyl outflow and thereby reduce the donor pool available for other methyl-transfer reactions, whereas loss of GNMT may lead to abnormal SAM accumulation and remodeling of both metabolic and epigenetic states.

(2) Methyl-donor-consuming role of NNMT

NNMT represents another class of small-molecule methyltransferases with methyl-sink characteristics. Increased NNMT can lower SAM or the SAM/SAH ratio and reduce certain histone or DNA methylation marks. Conversely, inhibition of NNMT helps improve methyl-donor availability and enhance certain methylation outputs.

Table 2. Major regulatory layers of the SAM cycle and methyl-transfer reactions

 

Regulatory Layer	Representative Node	Main Mechanism	Influence on Methyl-Transfer Reactions	Main Research Focus
Donor-formation layer	MAT1A/MAT2A	Determines the rate of SAM generation	Alters the size of the methyl-donor pool	Methionine utilization and regulation of MAT expression
Product-clearance layer	SAHH/AHCY	Clears SAH and relieves feedback inhibition	Maintains continuity of methyl-transfer reactions	SAH accumulation and inhibition of methylation
Regeneration and diversion layer	Remethylation, transsulfuration pathway	Determines the fate of homocysteine	Affects cycle closure and sulfur-metabolism output	Coupling between one-carbon metabolism and transsulfuration
RNA-processing layer	MAT2A-related splicing regulation	Regulates MAT2A homeostasis	Indirectly controls SAM levels	Post-transcriptional regulation of SAM homeostasis
Metabolic-sensing layer	SAMTOR	Senses SAM and links to growth signaling	Converts donor status into signaling status	Nutrient sensing and signal integration
Methyl-sink layer	GNMT, NNMT, etc.	Consumes SAM and redistributes methyl flux	Indirectly affects DNA/RNA/protein methylation	Methyl-donor buffering and metabolic competition

 

5. Research Strategies and Methodological Progress

5.1 Determination of cycle status

(1) Analysis should not rely on a single metabolite alone

Current studies of the SAM cycle should no longer remain at the level of measuring SAM or homocysteine alone. A more appropriate strategy is to analyze methionine, SAM, SAH, homocysteine, and related methylation readouts simultaneously, in order to distinguish among mechanisms such as donor insufficiency, product inhibition, limited regeneration, or increased methyl-sink activity.

(2) Parallel analysis of the metabolic layer and the modification layer

Measurement of cycle metabolites alone is still insufficient to explain functional consequences. Further integration with DNA, RNA, histone, or small-molecule methylation readouts is required. Only by examining the metabolic layer and the modification layer in parallel can a causal analytical framework linking "cycle status-methyl-transfer output-phenotypic change" be established.

 

5.2 Validation of key nodes

(1) Priority validation of MAT2A, SAHH, and methyl-sink enzymes

In mechanistic studies, nodes such as MAT2A, SAHH, GNMT, and NNMT have priority value for validation. They respectively represent three distinct modes of control: donor formation, product clearance, and methyl-flow buffering. These nodes can be used to distinguish whether changes in methylation arise from donor generation, product inhibition, or competitive consumption.

(2) Supplementary analysis of metabolic-sensing nodes

In studies involving nutrition, growth, or stress, metabolic-sensing nodes such as SAMTOR should also be included in the analytical framework. In these settings, changes in SAM may influence not only methylation itself, but also the broader metabolic state of the cell through nutrient-signaling pathways.

 

6. Typical Application Directions

6.1 Studies of epigenetic regulation

(1) SAM-cycle status can serve as an important interpretive framework for epigenetic modifications

In studies of DNA methylation, RNA methylation, and histone methylation, examination of methyltransferase expression alone is often insufficient to explain differences in final modification output. By determining methyl-donor formation, SAH-clearance efficiency, and the SAM/SAH ratio, the SAM cycle directly influences the driving force of methyl-transfer reactions. Therefore, incorporating SAM-cycle status into the analytical framework of epigenetic studies helps distinguish the relative contributions of "enzyme-level changes" and "donor-environment changes" to methylation phenotypes.

(2) Analysis of donor homeostasis improves mechanistic precision

When the research object involves DNA hypermethylation, increased RNA modification, or remodeling of histone methylation, lack of simultaneous analysis of SAM, SAH, methionine, and the relevant remethylation pathways generally makes it difficult to determine whether the changes arise from enhanced activity of methyltransferases themselves, expansion of the methyl-donor pool, reduced product inhibition, or reduction of methyl sinks. Therefore, analysis of the SAM cycle has gradually become an important component of increasing mechanistic interpretive power in studies of epigenetic modification.

 

6.2 Tumor and metabolic-reprogramming research

(1) Rearrangement of the SAM cycle is an important metabolic basis of aberrant methylation in tumors

Tumor cells are often characterized by increased methionine dependence, activated one-carbon metabolism, upregulated MAT2A, abnormal expression of NNMT or GNMT, and altered DNA/histone methylation patterns. These changes are not isolated from one another, but collectively point to reprogramming of the SAM cycle. Accordingly, the SAM cycle is not only a source system for methyl donors, but also an important hub linking nutrient dependence, epigenetic abnormality, and metabolic adaptation.

(2) Cycle nodes serve as interfaces linking metabolic intervention and epigenetic intervention

In tumor research, inhibition of DNA methyltransferases or histone methyltransferases alone can alter modification states, but if donor-layer changes are not simultaneously considered, differences in response to inhibitors across samples often remain difficult to explain. By contrast, joint analysis of MAT2A, SAHH, NNMT, remethylation pathways, and methylation-output layers is more conducive to establishing a complete mechanistic chain linking "metabolic state-donor homeostasis-methylation output-phenotypic response."

 

6.3 Neurobiology and aging research

(1) SAM-cycle homeostasis is closely related to maintenance of neural function

The nervous system is highly sensitive to one-carbon metabolism, methionine cycling, and methyl-donor homeostasis. Insufficient SAM supply, SAH accumulation, or reduced remethylation efficiency may all affect DNA/RNA methylation and the expression of genes related to neural function in neurons. Therefore, in studies of neurodevelopment, neurodegeneration, and cognitive function, the SAM cycle has become a metabolic control layer deserving particular attention.

(2) Age-related methylation drift can be interpreted in conjunction with changes in donor homeostasis

Aging is often accompanied by methylation drift, remodeling of nutrient-sensing pathways, and changes in redox state. If these phenomena are interpreted only from the perspective of methyltransferase expression, their metabolic basis is often inadequately captured. Incorporation of the SAM cycle into aging research helps explain how reduced donor formation, enhanced product inhibition, and redistribution of methyl sinks together drive altered methylation homeostasis.

 

6.4 Nutritional intervention and metabolic-regulation research

(1) The SAM cycle is the key intermediary layer through which nutritional input affects methylation output

Nutritional factors including methionine, folate, choline, betaine, serine, and vitamin B6 can all alter the operating state of the SAM cycle by influencing one-carbon metabolism and the fate of homocysteine. Therefore, the effects of nutritional intervention on methyl-transfer reactions are not merely the result of exogenous substrate supplementation, but reflect systemic regulation jointly achieved through donor generation, cycle regeneration, and branch competition.

(2) Nutrition-metabolism-epigenetics studies require support from cycle-level indicators

In studies of dietary intervention, metabolic reprogramming, and nutritional regulation, if the target phenotype involves methylation, gene expression, or metabolic adaptation, simultaneous evaluation of SAM, SAH, homocysteine, and related cycle nodes is generally required. Only by linking nutritional input with cycle status can the effects on methyl-transfer reactions and downstream phenotypes be interpreted more accurately.

 

7. Research Products Related to the S-Adenosylmethionine Cycle and Regulation of Methyl-Transfer Reactions

7.1 Basic metabolic and analytical reagents in studies of the S-adenosylmethionine cycle

 

Name	CAS No.	Experimental Stage	Key Use	Use Notes
L-Methionine	63-68-3	Donor-formation studies	Used as the starting substrate of the SAM cycle to analyze the effects of methionine supply on methyl-donor formation	Suitable for studies of methionine restriction, supplementation, and metabolic reprogramming
Adenosine	58-61-7	SAH hydrolysis and reflux studies	Used to analyze adenosine generation after SAH hydrolysis and its metabolic fate	Suitable for SAHH-related reactions and bypass-metabolism studies
ATP disodium salt	987-65-5	SAM-generation studies	Provides the energy source and adenosyl donor for the methionine adenosyltransferase reaction	Commonly used together with Mg2+ in in vitro MAT enzymology systems
S-Adenosyl-L-homocysteine	979-92-0	Product-inhibition studies	Used as the common product of methyl-transfer reactions to analyze feedback inhibition of methyltransferases by SAH	Suitable for paired analysis with SAM to evaluate methylation potential and the SAM/SAH ratio
L-Homocysteine	6027-13-0	Remethylation and diversion studies	Used to study homocysteine replenishment, remethylation, and diversion into the transsulfuration pathway	Suitable for studies of cycle closure and coupling with sulfur metabolism
Folic acid	59-30-3	One-carbon metabolism studies	Used to construct folate-dependent one-carbon-unit supply backgrounds	Suitable for studies of remethylation efficiency and coupling with the folate cycle
5-Methyltetrahydrofolate	134-35-0	Remethylation studies	Used as a methyl donor in homocysteine remethylation reactions	Suitable for validation of the MTR direction and studies of methionine regeneration
Betaine	107-43-7	Betaine-dependent remethylation studies	Used to analyze the contribution of the BHMT pathway to homocysteine recycling and SAM regeneration	Suitable for comparison of folate-dependent and folate-independent remethylation systems
Choline chloride	67-48-1	Choline-betaine donor studies	Used as a precursor of betaine to study the relationship between choline metabolism and methyl-donor homeostasis	Suitable for studies of nutritional background and methyl-donor reserve
L-Serine	56-45-1	One-carbon-unit supply studies	Used to analyze the contribution of serine-glycine metabolism to one-carbon-unit generation	Suitable for studies linking the entry point of one-carbon metabolism with the folate cycle
Glycine	56-40-6	One-carbon-metabolism coupling studies	Used to analyze serine/glycine interconversion and one-carbon-metabolism balance	Suitable for studies of nucleotide metabolism and the background of methyl-donor generation
L-Cysteine	52-90-4	Transsulfuration-pathway studies	Used to analyze product formation after diversion of homocysteine into sulfur-containing metabolic output	Suitable for studies linking the SAM cycle with glutathione metabolism
Reduced glutathione	70-18-8	Sulfur-metabolism output studies	Used to analyze changes in the antioxidant network after enhancement of the transsulfuration pathway	Suitable for studies linking the SAM cycle with redox homeostasis
Oxidized glutathione	27025-41-8	Redox-state studies	Used to evaluate the relationship between sulfur-metabolism output and changes in redox status	Suitable for paired analysis with reduced glutathione

 

7.2 Functional proteins and molecular tools in studies of the S-adenosylmethionine cycle and regulation of methyl-transfer reactions

 

Catalog No.	Name	Grade and Purity	Experimental Stage	Key Use	Use Notes
S1433377	S-Adenosylmethionine synthetase	—	SAM-generation studies	Used to construct in vitro enzymology systems for conversion of methionine to SAM	Suitable for studies of donor-formation efficiency, substrate limitation, and cycle entry
A1422763	Adenosylhomocysteinase	—	SAH-clearance studies	Used to analyze SAH hydrolytic capacity and its support for continuity of methyl-transfer reactions	Suitable for studies of product-inhibition relief, SAM/SAH balance, and cycle closure
rp188281	Recombinant Human Adenosylhomocysteinease/AHCY Protein	Carrier-free, His-tagged, ≥90%(SDS-PAGE), see COA	SAH-clearance studies	Used to establish recombinant AHCY/SAHH in vitro enzymology systems	Suitable for studies of SAH-clearance efficiency, relief of product inhibition, and mechanistic validation
Ab126379	Recombinant SAHH Antibody	Recombinant, ExactAb™, validated, see COA	Validation of the SAHH node	Used to detect changes in SAHH/AHCY protein expression	Suitable for correlational analysis between cycle status and methylation output
H1431695	Homocysteine methyltransferase	9012-40-2	Remethylation studies	Used to analyze remethylation capacity for converting homocysteine back to methionine	Suitable for studies of the cycle-regeneration layer and donor-regeneration efficiency
B1433319	Betaine homocysteine S-methyltransferase	9029-78-1	Betaine-dependent remethylation studies	Used to analyze the contribution of the BHMT direction to methionine regeneration and recovery of the SAM donor pool	Suitable for parallel comparison of folate-dependent and betaine-dependent remethylation
C1437067	Cystathionine γ-lyase	9012-96-8	Transsulfuration-diversion studies	Used to analyze the capacity for output of homocysteine into sulfur metabolism through the transsulfuration pathway	Suitable for studies of competition between cycle closure and the transsulfuration bypass
rp184904	Recombinant Human Glycine N-methyltransferase/GNMT Protein	Carrier-free, ≥90%(SDS-PAGE), see COA	Methyl-sink studies	Used to analyze the effects of GNMT on SAM consumption and methyl-donor buffering	Suitable for studies of methyl-flux redistribution and donor-pool homeostasis
Ab105966	GNMT Mouse mAb	ExactAb™, validated, carrier-free, 0.5 mg/mL	Validation of the GNMT node	Used to detect GNMT protein expression and regulatory changes	Suitable for validation of models with enhanced or suppressed methyl-sink activity
rp184926	Recombinant Human Nicotinamide N-Methyltransferase/NNMT Protein	Carrier-free, His-tagged, ≥95%(SDS-PAGE), see COA	Small-molecule methylation and methyl-sink studies	Used to analyze the effects of NNMT on SAM consumption and reduced methylation potential	Suitable for studies of metabolic competition, methyl-sink formation, and linkage to the epigenetic layer
N288820	NNMTi	≥95%	Studies of NNMT functional intervention	Used to inhibit NNMT activity and evaluate consumption of the donor pool by the small-molecule methylation branch	Suitable for combined use with GNMT, DNA methylation, and histone methylation readouts
EJ1512757	Mouse Nicotinamide-N-Methyltransferase (NNMT) ELISA Kit	BioReagent	Detection of NNMT levels	Used to detect changes in NNMT levels and assist analysis of enhanced methyl-sink states	Suitable for studies of methyl-donor competition in animal samples
EJ1514773	Human Adenosylhomocysteinase (AHCY) ELISA Kit	BioReagent	Detection of AHCY levels	Used to detect changes in AHCY/SAHH levels	Suitable for correlational analysis between SAH-clearance capacity and methylation potential
EJ1512877	Mouse Betaine Homocysteine Methyltransferase (BHMT) ELISA Kit	BioReagent	Detection of remethylation levels	Used to analyze changes at the node of the betaine-dependent remethylation pathway	Suitable for studies of donor-regeneration capacity and nutritional background
EJ1512276	Rat Cystathionine Beta Synthase (CBS) ELISA Kit	BioReagent	Detection of transsulfuration diversion	Used to detect CBS levels and evaluate the tendency for homocysteine to be diverted into the transsulfuration pathway	Suitable for studies of cycle closure and sulfur-metabolism allocation
EJ1513497	Human DNA Methyltransferase 1 (DNMT1) ELISA Kit	BioReagent	Detection of DNA-methylation output	Used to detect changes in the level of the maintenance DNA-methylation enzyme	Suitable for studies linking cycle status with DNA-methylation output
EJ1513496	Human DNA Methyltransferase 3A (DNMT3A) ELISA Kit	BioReagent	Detection of DNA-methylation output	Used to analyze changes in the levels of enzymes related to de novo DNA methylation	Suitable for studies of the effects of donor changes on establishment of DNA methylation
R126814	RG108	≥98%	Functional intervention in DNA methylation	Used to inhibit DNMT activity and analyze the response of the DNA-methylation output layer to cycle status	Suitable for combined interpretation with changes in the SAM/SAH ratio
S288597	SGI 1027	Moligand™, ≥98%(HPLC)	Functional intervention in DNA methylation	Used to inhibit DNA methylation and evaluate the relationship between the donor layer and the epigenetic layer	Suitable for control experiments involving DNA-methylation pathways
EJ1514308	Human Methyltransferase-like Protein 3 (METTL3) ELISA Kit	BioReagent	Detection of RNA-methylation output	Used to detect changes in METTL3 levels and evaluate the status of the RNA-methylation output layer	Suitable for studies linking SAM homeostasis to m6A writing
EJ1514310	Human Methyltransferase-like Protein 14 (METTL14) ELISA Kit	BioReagent	Detection of RNA-methylation output	Used to analyze changes in METTL14 and the status of the RNA-methylation complex	Suitable for validation of the RNA-methylation writing layer
EJ1514311	Human Methyltransferase-like Protein 16 (METTL16) ELISA Kit	BioReagent	Studies of RNA methylation and SAM sensing	Used to detect changes in METTL16 levels and assist analysis of its relationship to regulation of SAM homeostasis	Suitable for studies of cycle status and RNA-processing regulation
Ab116987	Recombinant m6A/N6-methyladenosine Antibody	See COA	RNA-methylation readout	Used to detect changes in m6A-modification levels	Suitable for directly linking donor-layer changes to RNA-methylation phenotypes
M1442317	mRNA Cap 2'-O-methyltransferase	—	RNA-methyltransfer studies	Used to establish in vitro reaction models for methylation of RNA cap structures	Suitable for SAM-dependent RNA-methyltransfer enzymology studies
EJ1514812	Human Protein Arginine N-methyltransferase 5 (PRMT5) ELISA Kit	BioReagent	Detection of protein-methylation output	Used to detect changes in PRMT5 levels and evaluate the status of the protein arginine-methylation layer	Suitable for studies of cycle status and protein-methylation output
EJ1514814	Human Protein Arginine N-methyltransferase 4 (PRMT4) ELISA Kit	BioReagent	Detection of protein-methylation output	Used to analyze changes in PRMT4-related methylation reactions	Suitable for comparative studies of protein arginine-methylation output
E276088	EPZ015866 (GSK591)	Moligand™, ≥98%	Studies of PRMT5 functional intervention	Used to inhibit activity of the PRMT5 complex and analyze the dependence of protein-methylation output on donor status	Suitable for control studies at the protein-methylation layer
A275769	AMI 1	≥98%	Intervention in protein arginine methylation	Used for broad-spectrum inhibition of protein arginine methyltransfer reactions	Suitable for overall intervention analysis at the protein-methylation output layer
EJ1514574	Human Histone-lysine N-methyltransferase 2D (KMT2D) ELISA Kit	BioReagent	Detection of histone-methylation output	Used to detect changes in KMT2D levels and analyze the status of the histone lysine-methylation layer	Suitable for studies of cycle status and chromatin modification
EJ1514575	Human Histone-lysine N-methyltransferase SETD7 (SETD7) ELISA Kit	BioReagent	Detection of histone-methylation output	Used to analyze changes in SETD7-related methylation reactions	Suitable for studies of individual lysine-methylation sites
B127141	BIX-01294	Moligand™, ≥98%	Functional intervention in histone methylation	Used to inhibit G9a/GLP-related H3K9 methylation output	Suitable for studies linking the donor layer to the histone-methylation layer
U275196	UNC0638	Moligand™, ≥98%	Functional intervention in histone methylation	Used to inhibit G9a/GLP activity and analyze changes in histone-methylation output	Suitable for parallel comparison with BIX-01294
C174641	CPI-1205	Moligand™, ≥97%	Studies of EZH2 functional intervention	Used to inhibit EZH2 and analyze responses of the H3K27 methylation output layer	Suitable for dual-factor studies combining cycle status and inhibitor treatment
G124898	GSK126	Moligand™, ≥98%	Studies of EZH2 functional intervention	Used to inhibit EZH2-related histone methylation	Suitable for comparative analysis of epigenetic output
G126541	GSK343	Moligand™, ≥98%	Studies of EZH2 functional intervention	Used to analyze the response of H3K27 methylation to changes in SAM donor status	Suitable for histone-methylation intervention in cell-based systems
G276508	GSK503	≥98%	Studies of EZH2 functional intervention	Used to supplement comparison of different EZH2-inhibition conditions	Suitable for comparative studies across different inhibitors
U125711	UNC1999	Moligand™, ≥98%	Studies of EZH2 functional intervention	Used to analyze changes in EZH2-dependent histone-methylation output	Suitable for linkage studies involving DNA/RNA methylation layers
P276093	PFI-2	Moligand™, ≥98%	Studies of SETD7 functional intervention	Used to analyze the response of the SETD7 output layer to donor changes	Suitable for refined mechanistic studies at the single-enzyme level

 

The relationship between the S-adenosylmethionine cycle and methyl-transfer reactions is not a linear process of "donor provision-product formation," but rather a dynamic regulatory network jointly determined by donor formation, product inhibition, cyclic regeneration, metabolic sensing, and competition from methyl sinks. Based on current research progress, nodes such as MAT2A, SAHH, GNMT, NNMT, METTL16, and SAMTOR represent key regulatory interfaces at different levels. Future efforts to achieve precise regulation of methylation reactions are therefore more likely to focus on hierarchical control of the SAM-homeostasis network rather than isolated enhancement or inhibition of single methyltransferases.

 

For more related articles, please see below:

[1] Roles of One-Carbon Metabolism Enzymes in Oxidative Stress and Epigenetic Regulation in Cardiovascular Diseases