title: Inhibition of the catalytic subunit of ram sperm adenylate cyclase by adenosine.
abstract: Adenosine inhibits ram sperm adenylate cyclase activity which is membrane-bound and comprises only the catalytic subunit. The inhibition parameters of adenylate cyclase by adenosine were not modified when the enzyme was purified 3 to 5,000 fold. Optimal inhibition by adenosine was found to require a high concentration of manganese, and exhibited a noncompetitive pattern up to a concentration of 1 mM adenosine. Adenosine was the most potent inhibitor among various analogs tested with the following rank order of potencies: adenosine greater than 2'O-methyladenosine greater than 2'deoxyadenosine much greater than 2 chloroadenosine. Studies with agonists and antagonists of the "R"-type adenosine receptor led us to conclude that adenosine inhibits ram sperm adenylate cyclase via a "P"-site carried by the catalytic subunit itself.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology*; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D007700:Kinetics; D008297:Male; D008345:Manganese / Q000494:pharmacology; D008566:Membranes / Q000201:enzymology; D012756:Sheep; D012995:Solubility; D013094:Spermatozoa / Q000201:enzymology*; D013329:Structure-Activity Relationship; D013737:Testis / Q000201:enzymology
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D008345:Manganese; D000241:Adenosine