Reconstitution of bovine procarboxypeptidase A-S6 from the free subunits

Abstract

The 3 subunits I, II and III, of bovine procarboxypeptidase A separated by reversible dimethylmaleylation can reassociate to form the reconstituted complexes I + II, I + III, and I + II + III. Since the association II + III is not possible, subunit I appears to play a central role in the formation of the complex. Subunit I probably possesses 2 independent and specific sites for the recognition of subunits II and III. The liberation of subunit I from any of the complexes was observed to increase its activability, although to a lesser extent than predicted by assays carried out with the succinylated protein. By contrast, the bound form of subunit II was activated faster than the free form. The potential activity of the bound form and the activity of the preformed endopeptidase were also higher, suggesting a conformational change induced by association. This suggestion was fully supported by the observed modifications of the heat stability and intrinsic fluorescence spectrum of the subunit resulting from association.