Acrosin: immunochemical demonstration of multiple forms generated from bovine and human proacrosin

A rabbit antiserum was prepared against purified bovine spermatozoal acrosin (EC 3.4.21.10), and the specific immunoglobulin G (IgG) was isolated by immunoaffinity chromatography. This IgG was shown to be monospecific for acrosin by rocket immunoelectrophoresis and by Western blotting of sodium dodecyl sulfate - polyacrylamide gels onto nitrocellulose sheets, followed by indirect immunodetection. In extracts of bovine spermatozoa prepared in the presence of 50 mM benzamidine, a single form of acrosin was detected, having a relative mass (Mr) of 48 000, which is presumed to be proacrosin. At least four further intermediate forms of acrosin were detectable in extracts prepared in the absence of benzamidine and in the various column eluates, having Mr values of 47 000, 44 000, 42 000, and 40 000, while the final product of the purification had a Mr of 37 500. The rabbit antibovine acrosin antiserum reacted also with human acrosin on Western blots. In this way, human proacrosin was found to have a Mr of 50 000 and to be convertible into intermediate forms of Mr 48 500, 44 500, 40 500, and 37 500, while the final product had a Mr of 35 500.