The hydrolysis by thermolysin of dipeptide derivatives that conatin substituted cysteine.

1. The preparation of protected dipeptides of the form acetylglycylamino acid amides is described, where the amino acid is phenylalanine, leucine, valine, alanine, S-methylcysteine, S-ethylcysteine, S-benzylcysteine and S-phenylcysteine. 2. Kinetic parameters for the thermolytic hydrolysis of these blocked dipeptides are reported. The rate of hydrolysis was fastest when the amino acid was leucine or phenylalanine, slower when it was S-methylcysteine, valine or S-ethylcysteine, much slower when it was alanine, and negligible for S-phenylcysteine or S-benzylcysteine. 3. The results are compared with those for similar dipeptide derivatives with benzyloxycarbonyl and furylacryloyl blocking groups, which are hydrolysed faster.