The Classification of Enzymes

Enzyme Class

1. Oxidoreductase

2. Transferase

3. Hydrolase

4. Lyase

5. Isomerase

6. Ligase

Examples of Enzymes

Dehydrogenases, oxidases, peroxidases Aminotransferases

Lipases/esterases, proteases, amidopeptidases, acylases, hydantoinases

Decarboxylases, dehydratases, aldolases, oxynitrilases Racemases, epimerases DNA ligase

Reactions Catalyzed

Oxidation/reduction reactions

Group transfer reactions (e.g., methyl, acyl, and phosphate) Hydrolysis (e.g., esters, amides, and hydantoins)

Additions to, or formation of, C=C, C=O, or C=N bonds Structural and geometric rearrangements Formation of C-C, C-N, C-O, or C-S bonds

D-Hydantoinase HN NH HN nh

OO | Alkaline pH

O D-W-carbamoylase ii Uh

,N CO2H

Hydantoin racemase

FIGURE 5.15 Industrial process for the production of (^)-^-hydroxyphenylglycine.

or an appropriate enzyme for a particular chemical synthesis and also to adapt the enzyme to specific reaction conditions. Several antibiotics based on the penicillin or cephalosporin structure contain (F)-4-p-hydroxyphenylglycine as the acyl side chain. This amino acid is produced on a multithousand tonne scale by dynamic kinetic resolution of the corresponding hydantoin (Figure 5.15).

Cell-free enzyme preparations offer advantages in simplicity of use, as well as tolerance to harsh conditions but suffer from the disadvantage of being expensive and may also need additional cofactors to function correctly. However, whole cells are relatively cheap and all necessary cofactors are present but product isolation can be complex and side reactions may also occur due to the presence of other enzymes in the cells. Fermentation using whole cell preparations is used extensively for production of bulk quantities of drugs such as antibiotics, steroids, ephedrine, cyclosporin, and vitamin B12.

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