Classification of Enzymes : Oxidoreducatases,Transferases,Hydrolases and Isomerases
Enzymes are classified on the basis of the reactions they catalyze- Each enzyme is assigned a four-digit classification number and a systematic name, which identifies the reaction catalyzed.
The international union of Biochemistry and Molecular Biology developed a system of nomenclature on which enzymes are divided in to six major classes, each with numerous sub groups. Enzymes are classified based on the reactions they catalyze.
Each enzyme is characterized by a code number comprising four digits separated by points. The four digits characterize class, sub-class, sub-sub-class, and serial number of a particular enzyme.
Class I. Oxidoreducatases
Enzymes catalyzing oxidation reduction reactions.
Example: Lactate-dehydrogenase
1- Lactic acid + NAD+ → Pyruvic acid + NADH+H+
Class II . Transferases:
Enzymes catalyzing a transfer of a group other than hydrogen (methyl, acyl, amino or phosphate groups)
Example: Enzymes catalyzing transfer of phosphorus containing groups.
ATP: D-hexose-6 phosphotransferase (Hexokinase)
ATP+D-Hexose → ADP+D-hexose-6-phosphate
Example: Acetyl-CoA: Choline D-acyltransferase (Choline Acyltransferase)
Class III. Hydrolases : Enzymes catalyzing hydrolysis of ester, ether, peptido, glycosyl, acid-anhydride, C-C, C-halide, or P-N-bonds by utilizing water.
Example: Enzymes action on glycosyl compounds
β-D- Galactoside galactohydrolase (β -Galactosidase)
α β -D- Galactoside+H2O alcohol +D-Galactose
Class IV. Lyases: Enzymes that catalyze removal of groups from substances by mechanisms other than hydrolysis, leaving double bonds.
Enzymes acting on C-C, C-O, C-N, C-S and C-halide bonds.
Example : Carbon-Oxygen lyases
Malate hydro-lyase (Fumarase)
COOH COOH
CHOH CH + H2O + H2O
CH2 HC
COOH COOH
Malate Fumarate
Class V. Isomerases :
Includes all enzymes catalyzing interconversion of optical, geometric, or positional isomers.
Example: Enzymes catalyzing interconversion of aldose and ketoses
D - Glyceraldehyde-3- phosphate ketoisomerase (triosephosphate isomerase)
D - Glyceraldehyde-3phosphate→ Dihydroxyacetone phosphate.
Read Also : Enzymes Definition : General Properties, Nature of Enzymes and All Explain About Enzymes
Class VI. Ligases or synthetases .
Enzymes catalyzing the linking together of 2 compounds coupled to the breaking of a pyrophosphate bond in ATP or similar trinucleotides: GTP, UTP etc. included are enzymes catalyzing reactions forming C-O, C-S, C-N, and C-C bonds, Example: Enzymes catalyzing formation of C-N-bonds
L- Glutamine: ammonia ligase (ADP) [Glutamine Synthetase]
ATP + L-Glutamate + NH4 = ADP + orthophosphate + L-Glutamine
Example: Enzymes catalyzing formation of C-C bonds
Acetyl-CoA: CO2 ligase (ADP) [acetyl-CoA carboxylase] ATP+ Acetyl-COA-CO2
Malonyl-CoA+ADP+pi.
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