Principles of Biochemistry (2+1)

8.1.5 ENZYME SPECIFICITY

Enzymes exhibit different levels of specificity for substrates. The degree of enzyme specificity is determined by the active site. Some active sites accommodate only one particular compound. While others can accommodate a “family” of closely related compounds.

Types of enzyme specificity:

1. Absolute specificity: Absolute specificity means an enzyme will catalyze a particular reaction for only one substrate. This most restrictive of all specificity is not common.

Urease is an enzyme with absolute specificity.

2. Stereochemical specificity: Such specificity means an enzyme can distinguish between stereoisomers. Chirality is inherent in an active site because amino acids are chiral compounds.

L-Amino-acid oxidase will catalyze reactions of L-amino acids but not of D-amino acids.

3. Group specificity: Such specificity involves structurally similar compounds that have the same functional groups. Chymotrypsin hydrolyses peptide bond in which the carboxyl group is contributed by aromatic amino acids such as tyrosin, tryptophan etc.Carboxypeptidase is group-specific; it cleaves amino acids, one at a time, from the carboxyl end of the peptide chain.

4. Linkage or bond specificity: Such specificity involves a particular type of bond, irrespective of the structural features in the vicinity of the bond. Phosphatases hydrolyze phosphate ester bonds in all types of phosphate esters. Pepsin, chymotrypsin and trypsin on peptide bonds. Linkage specificity is the most general of the specificities considered.

Group specificity