Substrate Specificity of Aqualysin I, a Bacterial Thermophilic Alkaline Serine Protease from Thermus aquaticus YT-1: Comparison with Proteinase K, Subtilisin BPN' and Subtilisin Carlsberg.

Aqualysin I is the alkaline serine protease isolated from an extreme thermophile, Thermus aquaticus YT-1. We analyzed kinetic properties of aqualysin I, using sixteen kinds of chromogenic succinyl-tripeptide p-nitroanilides as substrates. And we compared the substrate specificity of aqualysin I with those of proteinase K, subtilisin BPN', and subtilisin Carlsberg. We found that aqualysin I had three subsites, S1, S2, and S3, in the substrate binding site. S1 site preferred alanine and phenylalanine. S2 site preferred alanine and norleucine. And S3 site preferred phenylalanine and isoleucine. These specificities were similar to those of proteinase K and subtilisin BPN'. The specificity of subtilisin Carlsberg differed from those of other enzymes.