Reconstitution of the active form from the amino- and carboxyl-terminal fragments of a reactive site-modified subtilisin inhibitor of adzuki beans (Vigna angularis).

Abstract

The complex of an adzuki bean subtilisin inhibitor (ASI-II) with its target enzyme, prepared at pH 7.6, was subjected to reversed-phase HPLC in a trifluoroacetic acid-acetonitrile system. Two peptide fragments derived from the reactive site-modified ASI-II were obtained. The analyses of the amino acid composition and sequence of these two fragments revealed that one corresponded to the region from the amino-terminal Lys to the reactive site P1 Ala and the other, to the region from the reactive site P1' Asp to the carboxyl-terminal Gly of the inhibitor. Although neither fragment alone showed inhibitory activity against subtilisin, an equimolar mixture of both fragments was found to inhibit strongly the target enzyme, as did the intact inhibitor. Thus, it was suggested that the two fragments have strong specific affinity with each other, regenerating the reactive site-modified ASI-II, to inhibit the target enzyme.