Multiple GTP-binding proteins in sea urchin sperm: Evidence for Gs and small G-proteins.

Sea urchin sperm plasma membranes isolated from heads and flagella were used to examine the presence of Gs (stimulatory guanine nucleotide-binding regulatory protein) and small G-proteins. Flagellar plasma membranes incubated with [ P]NAD and cholera toxin (CTX) displayed radiolabeling in a protein of 48 kDa, which was reactive by immunoblotting with a specific antibody against mammalian Gs. CTX-catalyzed [ P]ADP-ribosylation in conjunction with immunoprecipitation with anti-Gs, followed by electrophoresis and autoradiography, revealed one band of 48 kDa.