The active centers of Streptomyces griseus protease 3 and alpha-chymotrypsin. Enzyme-substrate interactions beyond subsite S'1.

A series of N-acetylated tetra- to heptapeptide amides has synthesized for the study of enzyme-substrate interactions beyond the S1' subsite in Streptomyces griseus Protease 3 (SGP3) and alpha-chymotrypsin (EC 3.4.21.1). Evidence was obtained that S2'-P2' enzyme-substrate interactions can play a significant role for the rate of substrate hydrolysis in both enzymes. No important interaction could be demonstrated beyond the nitrogen atom of residue P3'. This provides supplementary evidence that the active site of SGP3 extends over 6-7 subsites and that of alpha-chymotrypsin over 5-6 subsites. SGP3 is a considerably more efficient protease than alpha-chymotrypsin, kcat/Km being approximately 5-10(6) S-1-M-1 for the best substrates, thus being about 100 times higher than for alpha-chymotrypsin. However, an analysis of the kinetic data indicates that, for both enzymes, the acylation rates for the best peptide substrates approach their deacylation rates.