Investigations on the substrate specificity of thermitase, a thermostable serine-protease from Thermoactinomyces vulgaris.

The kinetic parameters Km and kcat and the proteolytic coefficients kcat/Km for the hydrolysis of eighteen Z(benzyloxycarbonyl)-dipeptide methyl esters with variation of the residues in P1 and P2 position catalyzed by thermitase at pH 8 and 55 degrees C are reported. The results indicate that an integral part of both subsites, S1 and S2, are hydrophobic areas and that a mutual interaction between the side chains of P1 and P2 for optimal hydrolyisis does exist. Furthermore, the importance of the P2 for the peptidolytic activity of thermitase was shown using N-acylated oligo-alanine peptides and their p-nitroanilides. In all cases dialanine or alanine p-nitroanilide are the main products.