Selective enzymic methods for cleaving peptide bonds

9 Selective enzymic methods for cleaving peptide bonds 

It was mentioned above (Section 5.4) that trypsin cleaves lysyl and arginyl bonds so that, when a protein is exhaustively degraded by this enzyme, only one fragment can 

The use of thrombin, an enzyme that serves several roles in the blood-coagulating process, is a useful adjunct to tryptic hydrolysis. Its action is more specific and it cleaves only a limited number of arginyl bonds as a rule. Some arginyl bonds are only slowly hydrolysed by thrombin so that enzymic digests of protein can be quite complex in composition because degradation of substrate is incomplete. 

Chymotrypsin gives an alternative set of peptides because cleavage occurs at those peptide bonds which contain the carbonyl group of aromatic amino acids (Phe, Trp and Tyr) or hydrophobic aliphatic amino acids (Leu, Met and lie). Clearly, chy- 

Other less specific proteinases such as papain, subtilisin and pepsin are mainly of value for isolating small peptides containing disulphide bonds, phosphoserine or amino acids bearing carbohydrate attachments in their side-chain. 

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