MATURATION OF GUINEA-PIG SPERM IN THE EPIDIDYMIS INVOLVES THE MODIFICATION OF PROACROSIN OLIGOSACCHARIDE SIDE-CHAINS

Proacrosin from guinea pig cauda epididymal sperm has a lower molecular weight compared with the testicular zymogen. In this study, we have examined the structural basis of this change and where the conversion in proacrosin molecular weight occurs during sperm maturation. Immunoblotting of trifluoromethanesulfonic acid-deglycosylated testicular and cauda epididymal sperm extracts with antibody to guinea pig testicular proacrosin demonstrated that the polypeptide backbones of proacrosins from the testis and cauda epididymal sperm had the same molecular weights (almost-equal-to 44,000). Keratanase, an endo-beta-galactosidase specific for lactosaminoglycans, partially digested testicular proacrosin but had no effect on proacrosin from cauda epididymal sperm. In extracts of testis, caput epididymis, and corpus epididymis analyzed by immunoblotting, anti-proacrosin recognized a major antigen with an apparent molecular weight (M(r)) of 55,000, although a 50,000-M(r) minor antigen began to appear in the corpus epididymis. By contrast, extracts of cauda epididymis, vas deferens, and cauda epididymal sperm had the 50,000 M(r) protein as the only immunoreactive antigen. By enzymography following electrophoresis, the major bands of proteolytic activity in extracts of testis, caput epididymis, and corpus epididymis had 55,000 M(r). A band of protease activity with 55,000 M(r) also appeared in extracts of the corpus epididymis. However, the most prominent bands of proteolytic activity in cauda epididymis, vas deferens, and cauda epididymal sperm had 50,000 M(r). In addition, two other major protease activities were detected with 32,000 and 34,000 M(r); the relationships of these proteases to proacrosin are unclear. From these results, we conclude that the oligosaccharides of proacrosin are altered during epididymal transit land that this modification occurs in the corpus epididymis. Such structural alterations may be functionally significant, since sperm acquire the ability to fertilize eggs during epididymal maturation.