Detection of a sperm-coating antigen in the semen of Bubalus bubalis

Abstract 1. 1. Surface antigens of B. bubalis spermatozoa were solubilized by Triton X-100 and EDTA; the sperm extract was used to raise antibodies in rabbits. 2. 2. Two major polypeptides, immunoprecipitated from the seminal plasma by the antibodies against the sperm extract, exhibited the same electrophoretic mobilities of two immunorelated sperm surface antigens. 3. 3. The two polypeptides were isolated from the seminal plasma, by a multi-step chromatographic procedure, and found subunits of a single protein (MW 30,000), called SP 30. 4. 4. The SP 30 protein bound in vitro to the postacrosomal region of homologous spermatozoa from cauda epididymis. 5. 5. The localization of the sperm-coating antigen on the cell surface is compatible with a role in the fertilization process.