title: Characterization of a calmodulin-stimulated adenylate cyclase from abalone spermatozoa.
abstract: Abalone sperm adenylate cyclase activity is particulate in nature and displays a high Mg2+-supported activity (Mg2+/Mn2+ = 0.8) as compared to other sperm adenylate cyclases. Approximately 90% of the enzyme activity in crude homogenates is inhibited by EGTA in a concentration-dependent manner which is overcome by added micromolar free Ca2+. The EGTA-inhibited Ca2+-stimulated enzyme activity is also inhibited by phenothiazines. Added calmodulin, however, has no effect on enzyme activity prepared from crude homogenates. Preparation of a twice EGTA-extracted 48,000 X g pellet fraction yields a particulate enzyme activity that can be stimulated 10-65% by added calmodulin in the presence of micromolar free Ca2+. Detergent extraction (1% Lubrol PX) of the EGTA-washed 48,000 X g pellet solubilizes 2-5% of the total particulate adenylate cyclase activity, and this solubilized enzyme is activated up to 125% by calmodulin. The ability of the different enzyme preparations to be stimulated by calmodulin is inversely proportional to the endogenous calmodulin concentration. Calmodulin stimulation of the Lubrol PX-solubilized enzyme is specific to this Ca2+-binding protein and is mediated as an effect on the velocity of the enzyme. This stimulation is completely Ca2+ dependent and is fully reversible. These data suggest that the control of sperm cAMP synthesis by changes in Ca2+ conductance may be mediated via this Ca2+-binding protein.
mesh_terms: D000262:Adenylyl Cyclases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005476:Fluphenazine / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008974:Mollusca / Q000201:enzymology*; D000077423:Polidocanol; D011092:Polyethylene Glycols; D013094:Spermatozoa / Q000187:drug effects / Q000201:enzymology*; D014357:Trypsin / Q000378:metabolism
chemical_list: D002147:Calmodulin; D000077423:Polidocanol; D011092:Polyethylene Glycols; D004533:Egtazic Acid; D014357:Trypsin; D000262:Adenylyl Cyclases; D008274:Magnesium; D005476:Fluphenazine; D002118:Calcium