Monoclonal antibody to a membrane glycoprotein inhibits the acrosome reaction and associated Ca²⁺ and H⁺ fluxes of sea urchin sperm

Monoclonal antibodies were prepared using sea urchin (Strongylocentrotus purpuratus) sperm or isolated sperm plasma membrane vesicles as immunogen. Two monoclonal antibodies, J4/4 and J10/14, react with different epitopes on external domains of the same M_r = 210,000 integral-membrane glycoprotein. At Fab fragment concentrations of equivalent cell surface binding, J10/14 inhibits the egg jelly-induced exocytotic acrosome reaction and associated Ca²⁺ influx and H⁺ efflux, whereas J4/4 does not. Immunofluorescent localization shows that both monoclonal antibodies react with a narrow collar of plasma membrane over the acrosomal complex and also with the entire flagellum.