Peptides associated with eggs: mechanisms of interaction with spermatozoa.

Speract (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly), a peptide obtained from the culture medium of Strongylocentrotus purpuratus eggs, stimulates the respiration and motility of S. purpuratus spermatozoa under appropriate conditions. Resact (Cys-Val-Thr-Gly-Ala-Pro-Gly-Cys-Val-Gly-Gly-Gly-Arg-LeuNH2), a peptide obtained from Arbacia punctulata eggs also stimulates the metabolism and motility of A. punctulata spermatozoa, however, it fails to stimulate S. purpuratus spermatozoa. Early biochemical responses of the spermatozoa to the egg peptides include a net H+ efflux and elevations of cyclic AMP and cyclic GMP concentrations. In addition, in A. punctulata spermatozoa, a major plasma membrane protein is modified in response to resact such that its apparent molecular weight shifts from 160,000 to 150,000. If cells are incubated with 32P, the 160,000 molecular weight form of the protein becomes radiolabeled; subsequent addition of resact causes a rapid loss of 32P from the protein. The plasma membrane protein appears to be the enzyme, guanylate cyclase; coincident with the shift in apparent molecular weight, enzyme activity decreases by as much as 90%. Since speract fails to cause these responses in A. punctulata, it can be concluded that the events are receptor-mediated.