Identification of the Bovine Follicular Fluid Protein Involved in the in vitro Induction of the Hamster Sperm Acrosome Reaction

Abstract

Biochemical techniques were used to purify and identify the bovine follicular fluid protein involved in the in vitro induction of the acrosome reaction of hamster sperm. A follicular fluid protein fraction obtained by means of Sephadex G-150 and DEAE-Sephadex column chromatography, when combined with an Amicon XM-50 follicular fluid ultrafiltrate containing a motility factor, stimulated the acrosome reaction as effectively as intact follicular fluid. Further purification of the effective protein fraction by trichloroacetic acid precipitation and ethanol solubilization resulted in a highly purified preparation of serum albumin as identified by SDS [sodium dodecyl sulfate] disc-gel electrophoresis and immunoelectrophoresis. This highly purified albumin retains its full ability to induce the acrosome reaction in the presence of the XM-50 ultrafiltrate. The acrosome reaction inducing effectiveness of the albumin was dependent on its concentration. Similar treatment with trichloroacetic acid and ethanol further purified a crystalline bovine serum albumin to immunoelectrophoretic homogeneity and greatly increased its acrosome reaction inducing ability. This is the 1st demonstration that an appropriate treatment can greatly increase the acrosome reaction inducing ability of serum albumin which was previously a poor inducer of acrosome reactions. Albumin is probably the bovine follicular fluid protein involved in the in vitro induction of the hamster sperm acrosome reaction. The mechanism of action of albumin and/or its ligands in the acrosome reaction remains to be determined, but the mechanism appears to be more than just the maintenance of sperm viability and to require the presence of a sperm motility factor for optimal results.