title: Effects of PTH and Ca2+ on renal adenyl cyclase.
abstract: The effects of calcium ion on the adenylate cyclase system was studied in isolated, renal basal-lateral plasma membranes of the rat. Bovine parathyroid hormone (bPTH) and a guanyl triphosphate analogue, Gpp(NH)p were used to stimulate cyclase activity. Under conditions of maximal stimulation, calcium ions inhibited cyclic adenosine monophosphate (cAMP) formation, the formation rate falling exponentially with the calcium concentration. Fifty percent inhibition of either bPTH- or Gpp(NH)p-stimulated activity was given by approximately 50 microns Ca++. Also the Hill coefficient for the inhibition was close to unity in both cases. The concentration of bPTH giving half-maximal stimulation of cAMP formation (1.8 x 10(-8) M) was unchanged by the presence of calcium. These data suggest that calcium acts at some point other than the initial hormone-receptor interaction, presumably decreasing the catalytic efficiency of the enzymic moiety of the membrane complex.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007672:Kidney Cortex / Q000201:enzymology*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats
chemical_list: D010281:Parathyroid Hormone; D010446:Peptide Fragments; D006165:Guanylyl Imidodiphosphate; D000262:Adenylyl Cyclases; D002118:Calcium