Classification of enzymes

enzyme classification and nomenclature by International Union of Biochemistry and Molecular Biology

1. CLASSIFICATION OF ENZYMES MARIA K JOHN M.Sc. BIOTECHNOLOGY

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3. ENZYMES Enzymes are biological catalysts , which regulates the rate at which chemical reactions proceed without itself being altered in the process. Frederick W. Kühne gave the name ‘enzymes’ to the molecules detected by Eduard Buchner . Enzymology   is the branch of biochemistry aiming to understand how enzymes work, their kinetics, and structure. Central to every biochemical processes. Almost all enzymes are proteins, except catalytic RNA molecules(ribozymes).

4. Nomenclature of Enzymes Enzymes are commonly named by adding the suffix – ase to the name of their substrate or to a word describing their activity. The scheme for the systematic functional classification and nomenclature of enzymes was adopted by International Union of Biochemistry and Molecular Biology (IUBMB). Enzymes are classified and named according to the nature of the chemical reactions they catalyze. All enzymes were categorized into SEVEN major classes. Based on this classification, a ‘ four-digit unique number ’ (called EC number ) is assigned to each enzyme as an identification code.

5. Features 7 major classes. Each major class is divided into sub-classes. Each sub-class is further divided into sub-sub-classes. Each enzyme has been assigned a specific code number, called Enzyme Commission number (EC number). EC number consists of 4 digits, separated by points. For example , EC 2.7.1.1 is Hexokinase. Each digit in the EC number implies: First digit  Major class Second digit  Sub-class Third digit  Sub-sub-class Fourth digit  Systematic specific name of the enzyme. The systematic specific name consists of two parts: First part  name of the substrate Second part  nature of the reaction.

6. CLASSIFICATION

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8. OXIDOREDUCTASES (EC 1) Examples: Alcohol dehydrogenase, Oxidase

9. TRANSFERASES (EC 2) Examples: Transaminase, Hexokinase A-B + C  A + B-C

10. HYDROLASES (EC 3) Examples: Lipases, peptidases, phosphatases

11. LYASES (EC 4) Examples: Decarboxylase, dehydratases, aldolase

12. ISOMERASES (EC 5) Examples: Triose phosphate isomerases A-B-C  A-C-B

13. LIGASES (EC 6) Examples: DNA ligase, Aminoacyl tRNA synthetases A + B + ATP  AB + ADP+ Pi

14. TRANSLOCASES Example: ATP synthase

15. EC number Enzyme class Reaction type Examples EC 1 Oxidoreductases Oxidation-reduction reactions Alcohol dehydrogenase (EC 1.1.1.1) EC 2 Transferases Transfer of functional groups Transaldolase (EC 2.2.1.2), Transketolase (EC 2.2.1.1) EC 3 Hydrolases Hydrolysis reactions Cellulase (EC 3.2.1.4) EC 4 Lyases Group elimination to form double bonds Pyruvate decarboxylase (EC 4.1.1.1), Tryptophan synthase (EC 4.2.1.20) EC 5 Isomerases Isomerization Triose phosphate isomerase ( EC 5.3.1.1 ), Alanine racemase (EC 5.1.1.1) EC 6 Ligases Bond formation coupled with ATP hydrolysis Pyruvate carboxylase (EC 6.4.1.1),DNA ligase(EC 6.5.1.1), Carbamoyl phosphate synthetase I (   EC 6.3.4.16) EC 7 Translocases Movement of ions or molecules across membranes Cytochrome c oxidase ( EC 7.1.1.9 )

16. References McDonald, A.G., Boyce, S. and Tipton, K.F. ExplorEnz : the primary source of the IUBMB enzyme list.  Nucleic Acids Res.   37 , D593–D597 (2009). [ DOI:  10.1093/ nar /gkn582 ] http://expasy.org/enzyme Nelson, David L.  Lehninger Principles Of Biochemistry . New York : W.H. Freeman, 2008. Print . Voet , D., & Voet , J. G. (1995).  Fundamentals of Biochemistry . New York: J. Wiley & Sons . Berg, Jeremy M., John L. Tymoczko , Lubert Stryer , and Lubert Stryer . 2002.  Biochemistry . New York: W.H. Freeman .

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