| Abstract: | Speract (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly), a peptide obtained from eggs, has been shown to bind to a plasma membrane receptor of Lytechinus pictus spermatozoa. Here, we show that the addition of speract to intact cells caused the appearance of a new protein-staining band (Mr = 140,000) on sodium dodecyl sulfate (SDS) polyacrylamide gels; concomitantly, a protein of apparent molecular weight (Mr) 150,000 disappeared. Guanylate cyclase activity also decreased approximately 50% after the addition of speract to intact cells. Plasma membranes were subsequently prepared from spermatozoa in the presence of fluoride at pH 6.0, conditions that resulted in retention of the speract receptor and the Mr 150,000 protein. Addition of speract to the membranes resulted in a disappearance of the Mr 150,000 protein and the appearance of a Mr 140,000 protein. Coincident with the apparent change in molecular weight, guanylate cyclase activity decreased 30% at maximal speract concentrations. A physiological event that occurs in the intact cell in response to speract can now be reproduced in isolated plasma membranes; it should, therefore, now be possible to define the molecular events that occur as a result of speract: receptor interaction. |
