ISOLATION AND CHARACTERIZATION OF A PLASMA-MEMBRANE FRACTION FROM SEA-URCHIN SPERM EXHIBITING SPECIES-SPECIFIC RECOGNITION OF THE EGG SURFACE

A method was described for isolating preparative quantities of plasma membranes from sea urchin sperm. The final membrane fraction was homogeneous by sucrose density sedimentation and was enriched in adenylate cyclase as well as in the 4 glycoproteins accessible to radioiodination of intact sperm. The electrophoretic profiles of sperm membranes from 3 sea urchin species were very similar. The membrane preparation consists primarily of sealed vesicles which release carboxyfluorescein when exposed to detergenets or distilled water. Of the 125I-labeled vesicle material, 92% binds to wheat germ lectin columns, suggesting a right-side-out orientation. The isolated sperm membrane vesicles exhibited species specific adhesion to the surfaces of sea urchin eggs; this adhesion was blocked by pretreatment of the vesicles with trypsin or egg jelly. This method will be useful for isolating biologically active sperm membrane components involved in sperm-egg recognition during fertilization.