LOCALIZATION OF A HEPARIN-BINDING PROTEIN TO DISTINCT REGIONS OF BOVINE SPERM

Heparin-binding proteins (HBP) in bull seminal fluid bind to epididyma l sperm membranes at ejaculation. Peptides recognized by a monoclonal antibody (M1) correspond to proteins identified in complexes that have the greatest affinity for heparin and are present on sperm from bulls with higher fertility. Presence of specific HBP on sperm regulates th e ability of sperm to bind heparin, and heparin binding to sperm corre lates with the fertility potential of a bull. In these studies, the in teraction of HBP with sperm from 10 bulls of proven fertility was anal yzed by immunofluorescence of M1 to determine the localization of hepa rin-binding proteins during capacitation, and the fluorescent binding patterns were compared to bull nonreturn rates. Immunofluorescent loca lization of M1 binding sites revealed the existence of specific membra ne domains containing HBP in acrosomal and postacrosomal regions of ej aculated but not in epididymal sperm. Monoclonal antibody recognition of HBP localized on membranes of sperm revealed variable binding patte rns of M1 to the acrosomal region in sperm from bulls of known fertili ty. Regression analysis indicated a negative relationship between sper m displaying exclusively acrosomal fluorescence and bull nonreturn rat e. These data indicate that HBP bind to sperm in distinct patterns, on e of which differed among bulls of varying fertility, and indicate no apparent relocalization of these sites during cellular changes that oc cur in preparation for fertilization.