Active site of alpha-lytic protease: enzyme-substrate interactions.

The active site of alpha-lytic protease has been studied with a number of synthetic peptides and compared with similar data published for elastase. The kinetic data indicate that the active site of alpha-lytic protease extends over at least six subsites (S4--S2'). This extended active site has the effect of increasing kcat/Km by more than 10(6)-fold on going from an N-acetylated amino acid amide to a hexapeptide, due mainly to increases in kcat. There are major differences between alpha-lytic protease and elastase, both in terms of the kinetic parameters for a number of substrates and in terms of the tertiary structure of the active site. The ability of the S1 subsite to interact with various P1 amino acid side chains differs markedly between the two enzymes, and can be rationalized in terms of the tertiary structural differences. For alpha-lytic protease, enzyme-substrate interactions made in subsite S2 appears to be of primary importance, whereas subsite S4 is most important for elastase. The tertiary structural homology of alpha-lytic protease with another bacterial serine protease, Streptomyces griseus protease A, has allowed detailed model building of a tetrapeptide Ac-Pro-Ala-Pro-Ala-OH at the active site. In this way, the subsites S1--S4 have been examined for alpha-lytic protease and compared to other serine proteases.