Starfish acrosomal acid phosphatase: a cytochemical and biochemical study

The acrosome reaction of spermatozoa from the starfish Marthasterias glacialis was induced with the ionophore A23187. Reacted cells were then processed for acid phosphatase ultrastructural cytochemistry, but significant enzyme activity was not detected. However, when the supernates from suspensions of ionophore-treated sperm were assayed for acid phosphatase, a net enzyme activity was observed. Supernatant proteins were run in starch gel electrophoresis and fluorescent zymograms revealed a single band of acid phosphatase. SDS-PAGE of proteins eluted from the active spots of starch gels showed one major band of about 63 kDa. The results obtained support the hypothesis that the acid phosphatase whose activity has been detected only at the time of binding of sperm and egg originates from the sperm acrosome.