Removal of decapacitation factor from seminal plasma by high-speed centrifugation

The fertilizing ability of capacitated rabbit sperm is inhibited by mixing with seminal plasma; this is termed "decapacitation." The decapacitation factor was not destroyed or removed by freezing, heating to 65 C, or by prolonged dialysis, and was retained in the precipitate produced by the treatment of seminal plasma with 100% ethanol at –30 C. However, following centrifugation of seminal plasma for 3 hr or more at 105,000 g, the decapacitation activity disappeared. The disappearance of activity was not due to denaturation. Using spectrophotometry and moving boundary electrophoresis, no change could be detected in the protein components of the supernatants to account for the change in biological activity. It is concluded that the decapacitation effect of seminal plasma is related to a discrete molecule of large size. This may be protein, or conjugated with protein of a relatively heat-stable nature, which interacts with the active surface of the capacitated sperm head.