Isolation of an arbacia sperm fertilization antigen

Antisperm antibody fragments (IFab) block sea urchin fertilization by inhibiting the acrosome reaction and consequently sperm-egg attachment. We describe here a 68,000 dalton MW glycoprotein which neutralizes the fertilization-inhibiting action of IFab. This glycoprotein is a minor component is SDS-polyacrylamide gels of sperm membranes, but is greatly enriched in lithium diiodosalicylate extracts of the membranes. Final purification of the antigen was accomplished by elution from preparative SDS-polyacrylamide gels. This glycoprotein is evidently the sea urchin sperm receptor which interacts wih the egg jelly coat and acts as a "trigger" for the acrosome reaction.