Isolation of an “Immobilizing Antigen” from Rabbit Sperm Membranes

Abstract

To understand more precisely how individual sperm antigens function during sperm immobilization and fertilization, we describe a method for their isolation from rabbit sperm membranes. Three fractions were prepared by centrifugation of a rabbit epididymal sperm homogenate, examined by SDS-PAGE, and by electron microscopy, and tested for hyaluronidase and succinic dehydrogenase activity. The membrane-rich fraction was extracted with lithium diiodosalicylate and a sperm surface membrane glycoprotein (MGP; "immobilizing antigen") isolated from it by ion-exchange chromatography. The MGP showed a single immunodiffusion precipitin band against goat anti-rabbit sperm globulin. Antibodies to MGP immobilized rabbit sperm in the presence of complement. This MGP-"immobiizing antigen" was localized on the head and tail plasma membrane of epididymal, ejaculate and capacitated sperm by exchange agglutination and immobilization in the presence of guinea pig complement.