Answer to Question #89159 in Organic Chemistry for Phiroj Kumar bariha

Question

What are the various type of specifics exhibited by enzymes? Illustrate your answer with an example for each.

Answer 1

1) Relative, low or bond specificity. In this type the enzyme acts on substrates that are similar in structure and contain the same type of bonds e.g. a) amylase, which acts on alfa 1-4 glycosidic, bonds in starch, dextrin and glycogen. b) Lipase that hydrolyzes ester bonds in different triglycerides.

2) Moderate, structural or group specificity. In this type of specificity, the enzyme is specific not only to the type of bond but also to the structure surrounding it e.g. a) pepsin is an endopeptidase that hydrolyzes central peptide bonds in which the amino group belongs to aromatic amino acids e.g. phenyl alanine, tyrosine and tryptophan. b) Carboxypeptidase is an exopeptidase that hydrolyzes peripheral peptide bond at the carboxyl terminal of polypeptide chain.

3) Absolute, high or substrate specificity. In this type of specificity, the enzyme acts only on one substrate e.g. a)

lactase, which acts on lactose. b) Arginase, which acts only on arginine.

4) Optical or stereo-specificity. In this type of specificity, the enzyme is specific not only to the substrate but also

to its optical configuration e.g. a) L amino acid oxidase acts only on L amino acids. b) Alfa glycosidase acts only on alfa glycosidic bonds, which are present in starch, dextrin and glycogen.

5) Dual specificity. There are two types of dual specificity:

5.1) The enzyme may act on two substrates by  one reaction type:

e.g. xanthine oxidase enzyme acts on xanthine and hypoxanthine (two substrates) by oxidation (one reaction type).

5.2) The enzyme may act on one substrate by two different reaction types:

e.g. isocitrate dehydrogenase enzyme acts on isocitrate (one substrate) by oxidation followed by decarboxylation (two different reaction types).