Purification and characterization of an anti-sticking factor from goat epididymal plasma that inhibits sperm--glass and sperm--sperm adhesions

An anti-sticking factor (ASF-I) that showed high affinity for inhibiting adhesion of spermatozoa to glass was isolated from goat epididymal plasma and characterized. The factor was purified approx. 5600-fold and showed a single protein band when examined by non-denaturation and SDS-polyacrylamide gel electrophoresis. The molecular mass and S20w value of ASF-I were approx. 47 kDa and 4.25 S. ASF-I at a concentration of 1 nM showed nearly maximal anti-sticking activity when approx. 60% of the intact spermatozoa were prevented from adhesion to glass and it showed a high degree of protein specificity. Studies with trypsin and glycosidases demonstrated that both the sugar and protein parts of the molecule are essential for its anti-sticking activity. Evidence has been presented to support the view that the outer surface of sperm possesses specific ASF-I receptors that bind to 125I-labelled ASF and mediate cell adhesion to glass. ASF-I also showed high affinity for inhibiting agglutination of corpus-epididymal spermatozoa. The ASF activity was found to be distributed in all the tissues tested and its specific activity was markedly higher in blood plasma than in the tissues. The results suggest that ASF may play an important biological role by serving as a specific inhibitor of cell-substratum and cell-cell adhesions.