Angiotensin-Converting Enzyme (ACE): A Review of Molecular Features, Catalytic Functions, and Research and Translational Applications
Angiotensin-Converting Enzyme (ACE): A Review of Molecular Features, Catalytic Functions, and Research and Translational Applications
Angiotensin-converting enzyme (ACE) is a core metallopeptidase in the renin–angiotensin–aldosterone system (RAAS). It primarily converts angiotensin I (Ang I) into angiotensin II (Ang II) and can also degrade multiple bioactive peptides such as bradykinin, thereby playing pivotal regulatory roles in vascular tone, fluid and electrolyte homeostasis, inflammatory responses, and tissue remodeling. ACE is not only a classical drug target for hypertension, heart failure, and chronic kidney disease, but also an important molecular node in studies of endothelial function, fibrosis, immune–metabolic coupling, and peptide-network regulation. Research on ACE commonly spans isoform and domain-level differences, substrate scope and catalytic kinetics, regulation of tissue/cellular expression, and inhibitor pharmacology and biomarker development.
Keywords: angiotensin-converting enzyme; ACE; RAAS; Ang I/Ang II; bradykinin; zinc metallopeptidase; ACE inhibitors; endothelial function; fibrosis; biomarkers
I. Basic Concepts and Molecular-Biological Features of ACE
1.1 Definition and enzymological class
(1) ACE is a zinc-dependent dipeptidyl carboxypeptidase that removes dipeptides from the C terminus of peptide substrates. Its catalytic center depends on Zn2+ coordination and structural integrity of the active site.
(2) ACE is localized on the extracellular surface of the plasma membrane as a type I membrane protein. A soluble form also exists (released by shedding of the membrane-bound form and/or contributed by fluid compartments), and measurable activity is detected in plasma and tissue fluids.
1.2 Isoforms and domain organization
(1) Somatic ACE typically contains two homologous catalytic domains (the N-domain and the C-domain), which differ in substrate preference and inhibitor sensitivity.
(2) Testis ACE is commonly a single-domain form and is primarily associated with reproductive processes.
(3) Domain divergence enables a broader substrate spectrum and more complex physiological division of labor, providing a basis for domain-selective inhibitors and functional dissection studies.
1.3 Tissue distribution and cellular sources
(1) ACE is highly expressed on vascular endothelial surfaces, with the pulmonary microvascular bed contributing substantially to overall activity; accordingly, the lung circulation occupies an important position in Ang II generation and peptide metabolism.
(2) ACE is also expressed in the kidney, heart, vascular smooth muscle, and cells of the monocyte–macrophage lineage, contributing to local RAAS regulation and inflammatory microenvironment control.
(3) ACE expression is regulated by shear stress, hypoxia, inflammatory mediators, hormones, and metabolic states, exhibiting tissue specificity and pathology-dependent shifts.
II. Catalytic Functions and Pathway Frameworks
2.1 The RAAS main axis: conversion of Ang I to Ang II
(1) Reaction framework:
Angiotensinogen (liver-derived) is cleaved by renin to yield Ang I, which is further cleaved by ACE to generate Ang II.
(2) Ang II effects:
Ang II predominantly signals via the AT1 receptor to drive vasoconstriction, aldosterone secretion and sodium/water retention, and increased sympathetic activity. It can also induce oxidative stress, inflammation, and extracellular matrix deposition, contributing to cardiovascular and renal remodeling.
(3) Local RAAS:
Beyond the circulation, multiple tissues exhibit local generation and paracrine/autocrine effects, with ACE making a decisive contribution to local Ang II production and tissue remodeling.
2.2 Bradykinin and the kallikrein–kinin system: the complementary axis for vasodilation and inflammation control
(1) ACE degrades bradykinin. Bradykinin, via the B2 receptor, promotes nitric oxide (NO) and prostacyclin generation and exerts vasodilatory, anti-proliferative, and endothelial-protective effects.
(2) Increased ACE activity can both elevate Ang II and reduce bradykinin, creating a coordinated shift toward “constriction over dilation” and “pro-inflammatory over anti-inflammatory” states.
(3) Portions of the clinical and biological effects of ACE inhibitors are attributable to bradykinin elevation, which also provides mechanistic grounding for certain adverse effects and inter-individual variability.
2.3 Expanded substrate scope and peptide-network regulation
(1) Beyond Ang I and bradykinin, ACE contributes to the metabolism of multiple regulatory peptides, influencing vasoactivity, inflammatory signaling, and tissue homeostasis.
(2) Within a peptidomics framework, ACE can be viewed as a key “cleavage node” shaping the peptide landscape. Activity changes may drive system-level remodeling of peptide profiles.
III. Functional Distinction Between ACE and ACE2 and Key Points of Research Context
3.1 Directional differences in function
(1) ACE tends to promote Ang II generation and degrade bradykinin, biasing canonical RAAS toward “pro-constriction and pro-remodeling” directionality.
(2) ACE2 metabolizes Ang II to peptides such as Ang-(1–7), which, via Mas receptor pathways and related axes, generally exhibit vasodilatory, anti-inflammatory, and anti-fibrotic tendencies.
(3) In scientific reporting, it is essential to specify whether ACE or ACE2 is being discussed and to distinguish their directional roles within the RAAS network.
3.2 Metric selection and interpretive boundaries
(1) ACE expression, ACE activity, Ang II levels, and receptor expression do not necessarily change in parallel. Because RAAS is a multi-node network, a single metric rarely supports complete causal inference.
(2) In translational studies, combined measurements of ACE activity/expression, Ang I/Ang II, Ang-(1–7), AT1/AT2/Mas receptors, and downstream inflammatory and fibrotic markers are commonly required to establish a more complete evidence chain.
IV. Technical Routes for Measurement and Characterization
4.1 ACE activity assays
(1) Synthetic-substrate assays:
Use classical synthetic peptide substrates to quantify ACE cleavage rates, with spectrophotometric/fluorometric or chromatographic readouts. This approach is suitable for high-throughput screening and kinetic-parameter determination.
(2) Native or near-native substrate assays:
Quantify Ang I conversion and/or bradykinin degradation using LC-MS and related methods, improving physiological relevance and enabling complex-matrix applications.
(3) Key control variables:
As a Zn2+-dependent metallopeptidase, ACE is sensitive to chelators, ionic strength, and pH. Endogenous proteases, residual inhibitors, and protein-binding effects in samples can confound results; blanks, spike-recovery tests, and inhibitor-validation controls are required.
4.2 ACE protein and expression measurements
(1) Immunological methods:
Western blot, ELISA, and immunohistochemistry quantify and localize ACE protein. Attention should be paid to domain- and glycosylation-dependent antibody recognition differences.
(2) Transcript-level assays:
QPCR and transcriptomics quantify ACE gene-expression changes, but nonlinearity between transcription and membrane-surface activity must be considered.
(3) Cell-surface and soluble ACE:
Flow cytometry can profile cell-surface ACE, while soluble ACE in body fluids requires interpretation of shedding mechanisms and sources in conjunction with activity measurements.
4.3 RAAS peptide profiling and pathway readouts
(1) Quantification of Ang I/Ang II/Ang-(1–7):
Prioritize high-selectivity LC-MS or high-specificity immunoassays, supported by calibration curves and internal-standard strategies to improve comparability.
(2) Downstream signaling:
The AT1 axis is commonly associated with ROS generation, inflammatory mediator expression, and upregulation of fibrosis-related genes (e.g., collagens and the TGF-β axis). Molecular markers and functional assays should be used in parallel for validation.
V. Research Application Scenarios
5.1 Hypertension and vascular-function research
(1) Mechanistic studies:
Use ACE activity modulation as an upstream perturbation and combine vascular reactivity assays, endothelial-function assessments (NO bioavailability and eNOS-related metrics), and RAAS peptide profiling to dissect mechanisms controlling vascular tone and structural remodeling.
(2) Model applications:
In spontaneous hypertension models, salt-sensitive models, or vascular injury models, the ACE/Ang II axis is often a key variable. The bradykinin axis and local RAAS should also be assessed to avoid overinterpretation from a single-axis perspective.
5.2 Cardiac remodeling and heart failure
(1) Ang II-driven remodeling:
Ang II promotes cardiomyocyte hypertrophy, fibroblast activation, and collagen deposition. ACE inhibition can serve as a pharmacological tool to validate Ang II-driven remodeling hypotheses.
(2) Evaluation framework:
Integrating cardiac functional testing, histological fibrosis quantification, inflammatory and oxidative-stress markers, and RAAS peptide profiling strengthens causal inference.
5.3 Chronic kidney disease and glomerular–interstitial injury
(1) Local RAAS:
Renal ACE/Ang II can promote glomerular hypertension, proteinuria, and interstitial fibrosis. Spatial patterns of ACE activity and receptor expression in the kidney often shape disease-progression modes.
(2) Translational relevance:
Association studies linking ACE-related metrics to renal-function decline and fibrotic markers can support target evaluation and stratification strategies.
5.4 Cross-disciplinary studies of inflammation, immunity, and fibrosis
(1) Immune-cell ACE:
ACE expression in monocyte–macrophage lineage cells may influence local Ang II generation and inflammatory cascades, shaping fibrotic microenvironments.
(2) Coupling to fibrotic pathways:
The Ang II axis is strongly coupled to TGF-β/Smad, NF-κB, and oxidative-stress pathways. Multi-omics and pharmacological perturbations can be used to interrogate network structure.
5.5 Pharmacology and inhibitor screening
(1) ACE inhibitor screening:
Synthetic-substrate high-throughput activity screening can be used as an entry point, followed by validation of selectivity, kinetic parameters, and cell/tissue-level effects. Distinguish in vitro inhibitory potency from cellular/in vivo exposure–response relationships.
(2) Domain-selective studies:
Domain-selective inhibitors and/or mutant constructs targeting N-domain versus C-domain differences help separate ACE contributions across substrate pathways.
(3) Natural products and peptide inhibitors:
Food-derived peptides and natural products are frequently studied as ACE inhibitors. Study designs should strengthen stability, specificity, and in vivo effectiveness validation and avoid extrapolating functional conclusions solely from in vitro IC50 values.
VI. Industry and Clinical-Translational Application Frameworks
6.1 Biomarkers and risk stratification
(1) Plasma soluble ACE activity or concentration can serve as an associative marker in certain disease contexts, but interpretation is complicated by heterogeneous sources and shedding mechanisms; joint analysis with RAAS peptide profiles and clinical phenotypes is recommended.
(2) Genetic polymorphisms and inter-individual variability can influence ACE levels and drug responses; translational studies often include genetic background as a stratification variable.
6.2 Mechanistic and safety context for drug actions
(1) Effects of ACE inhibition arise from both Ang II reduction and bradykinin elevation-mediated endothelial-protective pathways; mechanistic studies should support this linkage by jointly measuring receptor axes and peptide levels.
(2) Bradykinin-linked adverse-effect risk implies that kallikrein–kinin system readouts should be monitored in pharmacological models to improve interpretability and translational relevance.
VII. Practical Considerations for Research Use and Experimental Design
7.1 Building a metric system and maintaining causal-chain completeness
(1) It is recommended to co-design measurements of ACE activity/expression with RAAS peptide profiling (Ang I, Ang II, Ang-(1–7)) and receptor-axis readouts (AT1/AT2/Mas), avoiding inference of the entire pathway state from a single ACE metric.
(2) At the tissue level, distinguish circulating RAAS from local RAAS, particularly because spatial heterogeneity in the heart, kidney, and vascular wall can materially affect conclusions.
7.2 Matrix and interference control in activity assays
(1) Body fluids and tissue homogenates may contain endogenous proteases and inhibitors, and sample processing can introduce chelators or denaturants, all of which can yield underestimated ACE activity or false-positive/false-negative results.
(2) Include inhibitor-specificity controls, spike recovery, and dilution back-calculation consistency checks, and add bridging QC samples in cross-batch comparisons.
7.3 Comparability requirements in pharmacological-intervention studies
(1) Inhibitor dose, dosing window, and exposure levels determine effect size; incorporate PK–PD relationships into study design rather than comparing groups based only on nominal doses.
(2) If conclusions involve fibrosis or remodeling, add time-series sampling and histological quantification beyond endpoint markers to support causal inference.
VIII. Aladdin-Related Products
8.1 Core Proteins and Angiotensin Peptides in the ACE/RAAS Pathway (Including Standards, Analogs, Fragments, and Conjugates)
Catalog No. | Product Name | CAS No. | Grade and Purity |
[Ile7]-Angiotensin III | 102029-49-2 | ≥98% | |
[Val5]-Angiotensin II acetate salt hydrate | 5649-07-0 | ≥97%(HPLC) | |
Angiotensin I human acetate salt hydrate | 70937-97-2 | ≥97% | |
Human angiotension Ⅱ Relative Molecular Weight | 4474-91-3 | Moligand™, Angiotensin II:1045.5 | |
Angiotensin 1-7 | 51833-78-4 | 10mM in Water | |
Angiotensin (1-7) (acetate) | 51833-78-4 (free) | ≥98% | |
Angiotensin II human Acetate | 68521-88-0 | ≥98% | |
Angiotensin II human Acetate | 68521-88-0 | 10mM in Water | |
Angiotensin III TFA | 12687-51-3 (free) | ≥98% | |
Angiotensin III, human, mouse（Acetate） | 13602-53-4 (free) | Moligand™, ≥98% | |
Angiotensin A TFA | 51833-76-2 (free) | ≥98% | |
Angiotensin I/II (3-7) | 122483-84-5 | ≥99% | |
Angiotensin Ⅱ, human | 4474-91-3 | Moligand™, ≥90% | |
Angiotensin II/BSA | -- | -- | |
Angiotensin I/BSA | -- | -- | |
Angiotensin II human Acetate | 68521-88-0 | ≥98% | |
Angiotensin Itrifluoroacetate | 484-42-4 (free) | ≥98% | |
Angiotensinogen, Human Plasma | 11002-13-4 | BioReagent, Native, ≥95%(SDS-PAGE), Pre-lyophilization Protein Concentration | |
Angiotensin Converting Enzyme (ACE) from Porcine lung | 9015-82-1 | Bioactive, ActiBioPure™, High Performance, EnzymoPure™, ≥0.05 U/mg powder | |
Angiotensin Ⅱ acetate | 4474-91-3 (free base) | Moligand™, ≥98% | |
(Sar1,Gly8)-Angiotensin II TFA | 100900-29-6 (free base) | ≥98% |
8.2 Key Reagents Commonly Used for ACE Activity Assays and RAAS Peptidome Verification
Category | Reagent Name | CAS No. | Workflow Step | Role in the System | Use Notes |
Kinin-axis substrate | Bradykinin | Kinin degradation readout | ACE-degradable substrate used to assess ACE-mediated kinin degradation and validate “ACE inhibitor → bradykinin accumulation” directionality | Rapid sampling and quench; run time gradients; include matrix blanks and spike recovery | |
ACE inhibitor (positive control) | Captopril | Inhibitor validation | Positive control to establish inhibition window and assay sensitivity (IC50 / dose–response) | Fix solvent fraction; include solvent controls; prepare fresh or aliquot and store frozen | |
Quench / metal-dependence control | EDTA (disodium salt) | Quench/background control (optional) | Chelates metal ions to rapidly stop reactions or serve as a control for metal dependence and non-specific background | Fix quench conditions; include paired “±EDTA” controls; avoid carryover into downstream metal-dependent steps | |
Metal-dependence control | EGTA | Metal-dependence control (optional) | Preferential Ca2+ chelator used as control/quench tool to assess divalent-ion contributions to background and stability | Choose either EGTA or EDTA and standardize; validate interpretability with parallel controls | |
Reaction buffer | Tris (tris(hydroxymethyl)aminomethane) | Activity-assay buffer | Stabilizes pH and ionic environment to reduce drift-driven changes in apparent ACE rates | pH is temperature-dependent; standardize temperature and pH-calibration approach | |
Reaction buffer | HEPES | Activity-assay buffer | Provides more stable buffering in cell/membrane-protein contexts, reducing rate bias from pH drift | Lock ionic strength together with buffer; maintain consistency across batches | |
Ionic-strength control | Sodium chloride (NaCl) | Condition-window scanning | Tunes ionic strength to evaluate salt sensitivity of apparent ACE activity, substrate binding, and inhibitor effects | Map salt gradients first, then lock conditions; keep conditions identical for comparative studies | |
Zn-dependence condition check | Zinc chloride (ZnCl2) | Condition check (optional) | Tests sensitivity of assay performance to zinc/metallopeptidase-related metal environments (as needed) | Use low-dose gradients; watch for metal-catalyzed side-reaction background | |
Zn-dependence condition check | Zinc sulfate (ZnSO4) | Condition check (optional) | Same purpose as above for evaluating zinc-ion condition effects | Choose either ZnCl2 or ZnSO4; keep counterion background consistent for interpretability | |
Sample handling (non-target protease suppression) | PMSF | Body-fluid/tissue-homogenate handling (optional) | Inhibits serine proteases to reduce interference from non-target proteases in substrate/peptide readouts | Prepare fresh and use briefly; verify recovery with “±inhibitor” controls; check platform compatibility | |
Sample handling (non-target protease suppression) | Benzamidine | Body-fluid sample handling (optional) | Inhibits trypsin-like proteases to reduce background cleavage in body fluids | Match to sample type; verify with parallel controls | |
Carrier/solvent | DMSO | Inhibitor preparation | Solubilizes candidate inhibitors and serves as dosing carrier to improve screening reproducibility | Fix final concentration; include solvent controls; avoid high fractions that affect enzyme activity | |
Anti-adsorption/stability | BSA | Low-concentration systems (optional) | Reduces peptide/protein adsorption to tube and well surfaces, improving repeatability at low concentrations | Include blank subtraction; prefer low-endotoxin grade when relevant | |
Quench/deproteinization | Trichloroacetic acid (TCA) | Reaction quench/deproteinization | Stops enzymatic reactions and removes proteins to improve downstream detection (LC/MS, chromatography) | Standardize neutralization/dilution after quench; evaluate recovery | |
Quench/acidification | Formic acid | LC-MS sample prep | Acidifies and stabilizes samples and suppresses residual enzyme activity, improving LC-MS compatibility | Fix final concentration; add with internal standards for higher robustness | |
LC solvent | Acetonitrile | LC separation | Reversed-phase LC gradient solvent to improve separation and peak shape | Standardize gradients and lots; monitor system drift | |
HPLC additive | TFA | Peak-shape improvement (as needed) | Improves peak shape/separation in some HPLC systems (more suited for HPLC-UV) | Use cautiously with MS (ion suppression); choose either TFA or formic acid and standardize | |
Immunoassay wash/background reduction | Tween 20 | ELISA/immunoassays | Reduces non-specific adsorption background and improves signal-to-noise | Fix concentration; avoid excessive amounts that impair binding |
As a key catalytic node in RAAS, ACE exerts central influence over vascular tone regulation, fluid homeostasis, inflammatory responses, and tissue remodeling by promoting Ang II formation while degrading bioactive peptides such as bradykinin. It is therefore a canonical target in cardiovascular and renal translational research and pharmacological intervention studies. In research practice, the credibility of ACE-related conclusions depends on rigorous interference control in activity and expression measurements, clear separation of circulating versus local RAAS, and integrated validation across peptide profiles, receptor-axis readouts, and downstream pathological phenotypes. An “ACE–peptidome–receptors–phenotype” integrated design is recommended to build an evidence chain that is reproducible, comparable, and mechanistically interpretable.