liminfoEnzyme Commission Reference
Free reference guide: Enzyme Commission Reference
About Enzyme Commission Reference
The Enzyme Commission (EC) Number Reference is a comprehensive guide to the IUBMB enzyme classification system covering all 7 major enzyme classes: EC 1 Oxidoreductases, EC 2 Transferases (including kinases), EC 3 Hydrolases (proteases, phosphatases, lipases), EC 4 Lyases, EC 5 Isomerases, EC 6 Ligases, and EC 7 Translocases (added 2018 for membrane transport enzymes). The 4-level EC numbering system (EC A.B.C.D) is explained with practical examples.
Key enzyme entries detail protein serine/threonine kinases (EC 2.7.11.1 including PKA, PKC, CDK, MAPK, Akt), receptor tyrosine kinases (EC 2.7.10.1 including EGFR, HER2, VEGFR), serine proteases (EC 3.4.21 with catalytic triad Ser-His-Asp), cysteine proteases (EC 3.4.22 including caspases), aspartate proteases (EC 3.4.23 including HIV protease), LDH (EC 1.1.1.27), peroxidase/HRP (EC 1.11.1.7), ALP (EC 3.1.3.1), and DNase I (EC 3.1.21.1).
Enzyme kinetics sections cover Michaelis-Menten equation (Km, Vmax, kcat, catalytic efficiency kcat/Km), inhibition types (competitive, noncompetitive, uncompetitive, mixed), Lineweaver-Burk double reciprocal plots, and allosteric regulation (Hill equation, cooperativity). Database guides for BRENDA, KEGG Enzyme, ExPASy ENZYME, and UniProt enzyme search complete the reference.
Key Features
- All 7 EC enzyme classes with subclass breakdowns: oxidoreductases through translocases (2018)
- 4-level EC numbering system (EC A.B.C.D) explained with reaction types and substrate specificity
- Protein kinases (PKA, PKC, CDK, MAPK, Akt) and receptor tyrosine kinases (EGFR, HER2, VEGFR) with inhibitor examples
- Protease families: serine (trypsin, thrombin), cysteine (caspases), and aspartate (pepsin, HIV protease) with catalytic mechanisms
- Clinical enzymes: LDH isoenzymes, ALP tissue types, HRP ELISA substrates, and DNase I applications
- Michaelis-Menten kinetics: Km substrate affinity, Vmax, kcat turnover number, and catalytic efficiency
- Four inhibition types (competitive, noncompetitive, uncompetitive, mixed) with Lineweaver-Burk plot patterns
- Enzyme databases: BRENDA kinetic data, KEGG pathway mapping, ExPASy nomenclature, UniProt sequence/function search
Frequently Asked Questions
What are the 7 EC enzyme classes?
EC 1 Oxidoreductases (redox reactions), EC 2 Transferases (group transfer, includes kinases), EC 3 Hydrolases (bond cleavage with water), EC 4 Lyases (non-hydrolytic bond cleavage), EC 5 Isomerases (structural rearrangement), EC 6 Ligases (ATP-coupled bond formation), and EC 7 Translocases (membrane transport, added in 2018 for enzymes like Na+/K+-ATPase and ABC transporters).
How does the EC numbering system work?
EC numbers follow a 4-level format (EC A.B.C.D): A is the main reaction type (1-7), B specifies the functional group or substrate subclass, C indicates the specific substrate or coenzyme, and D is the serial number for the specific enzyme. For example, EC 2.7.11.1 means transferase (2), phosphotransferase (7), serine/threonine kinase (11), non-specific (1).
What protein kinases are covered?
EC 2.7.11.1 Protein-serine/threonine kinases include PKA (cAMP-dependent), PKC (Ca/lipid-dependent), CDK (cyclin-dependent), MAPK (ERK, JNK, p38), Akt/PKB, and CK2. EC 2.7.10.1 Receptor tyrosine kinases include EGFR, HER2, VEGFR, PDGFR, FGFR, and Insulin Receptor, with clinically important inhibitors like Imatinib, Gefitinib, and Sunitinib.
What are the different protease families?
Three major families are detailed: Serine proteases (EC 3.4.21) with the Ser-His-Asp catalytic triad, including trypsin, chymotrypsin, elastase, and thrombin, inhibited by PMSF/Aprotinin. Cysteine proteases (EC 3.4.22) including papain and caspases (key in apoptosis), inhibited by E-64 and Z-VAD-FMK. Aspartate proteases (EC 3.4.23) with acidic pH optimum, including pepsin, renin, HIV protease, and BACE.
How is Michaelis-Menten kinetics explained?
The equation v = Vmax[S]/(Km + [S]) is explained with Km as substrate concentration at half-Vmax (lower Km = higher affinity). kcat (turnover number) = Vmax/[E]total, and kcat/Km measures catalytic efficiency with a diffusion limit of 10^8-10^9 M-1s-1. Examples include hexokinase (Km = 0.1 mM glucose) vs glucokinase (Km = 10 mM).
What enzyme inhibition types are covered?
Four types are explained: Competitive (competes with substrate, Km increases, Vmax unchanged, e.g., Methotrexate vs DHFR), Noncompetitive (Km unchanged, Vmax decreases), Uncompetitive (binds only ES complex, both Km and Vmax decrease), and Mixed (both change). Lineweaver-Burk plot patterns distinguish each type by changes in slopes and intercepts.
What enzyme databases are referenced?
BRENDA (brenda-enzymes.org) provides Km, kcat, Ki values, optimal pH/temperature, inhibitors, and disease links. KEGG Enzyme maps enzymes to metabolic pathways with REST API access. ExPASy ENZYME offers nomenclature and historical EC number tracking. UniProt allows enzyme searching by EC number with sequence, active site, mutation, and GO annotation data.
What clinical enzyme applications are included?
LDH (EC 1.1.1.27) isoenzymes LDH1-5 for cardiac/hepatic markers (normal 140-280 U/L). ALP (EC 3.1.3.1) isoenzymes for bone/liver disease (normal 44-147 U/L). HRP (EC 1.11.1.7) as ELISA detection enzyme with TMB/DAB/ECL substrates. DNase I (EC 3.1.21.1) for footprinting, RNA extraction DNA removal, and DNase-seq chromatin accessibility analysis.