3.1.2. Enzyme Classification

There are approximately 3000 known enzymes. These enzymes are classified into six categories based on the type of reaction they catalyze.

1. Oxidoreductase: Oxidizes or reduces by transfer of hydrogen or electrons.
(a) dehydrogenases:

(b) oxidases:


(c) peroxidases:


(d) oxygenases:


2. Transferase: Transfers C-, N-, P-, or S-containing functional groups such as aldehydes and ketones, glycosils, acyls, phosphates, and sulfur containing groups.

3. Hydrolase: Hydrolyzes esters, anhydrides, peptide bonds, other C-N bonds, glycosides.

4. Lyase: Adds to double bonds:

> C = C <

> C = O

> C = N

5. Isomerase: Isomerizes optical isomers

6. Ligase: Splits C-C, C-O, C-N, C-S and C-halogen bonds without hydrolysis or oxidation, mostly with ATP.