Inhibition of various proteases by MAPI and inactivation of MAPI by trypsin

Abstract

MAPI (microbial alkaline protease inhibitor) was isolated from culture broth of Streptomyces chromofuscus SMF28. The K(i) values of MAPI for the representative serine proteases such as chymotrypsin and proteinase K were 0.28 and 0.63 μM, respectively, and for the cysteine proteases cathepsin B and papain were 0.66 and 0.28 μM, respectively. These data indicate that MAPI is not a potent selective inhibitor of serine or cysteine proteases. Progress curves for the inhibition of three proteases by MAPI exhibited characteristic patterns: MAPI exhibited slow-binding inhibition of cathepsin B. It was rapidly associated with chymotrypsin before the addition of substrate and then reactivation of MAPI-inhibited enzyme was investigated in the presence of substrate. On the other hand, MAPI-proteinase K interaction was typical for those classical inhibitors. When MAPI was incubated with trypsin, there was an extensive reduction in the inhibitory activities of MAPI corresponding to 66.5% inactivation of MAPI, indicating that trypsin- like protease may play a role in the decrease of the inhibitory activity during cultivation.