title: Effects of Mg2+, Mn2+ and Ca2+ on adenylcyclase activity. Evidence for a metallic site.
abstract: In membrane preparations from immature erythrocytes from rats the effects of the divalent cations Mg2+, Mn2+ and Ca2+ on basal activity of adenylcyclase as well as on enzyme activity stimulated by isoprenaline (Ipn) or guanylyl-imidodiphosphate [Gpp(NH)p] were investigated.--Mn2+ is a ten-fold stronger activator of the enzyme than Mg2+ irrespective of the stimulant used. At suboptimal concentrations of the cations at all concentrations of Gpp(NH)p used (10(-6) to 10(-3) M) reaction velocities increase progressively over an incubation period of 40 min. Optimal cation concentrations, however, i.e. 3 x 10(-3) M Mn2+ and 3 x 10(-2)M Mg2+ elicit a constant and at 10(-4) M Gpp(NH)p maximal reaction velocity. In contrast, the Ipn-stimulated  cAMP synthesis proceeds linearly at all Ipn concentrations used; a change of cation concentrations elicits only a change in reaction velocity, which is maximal at 10(-3) M Mn2+ and 10(-2) M Mg2+ respectively.--Ca2+ inhibits adenylcyclase activity in a non-competitive manner, irrespective of the stimulant and ion concentration used. The Mg2+-activated enzyme, however, is more susceptible to the inhibiting effect of Ca2+ than the Mn2+-activated enzyme.--It is concluded that Mn2+ and Mg2+ are allosteric effectors of the enzyme adenylcyclase, acting at a Me2+-site of the catalytic unit of adenylcyclase.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D000242:Cyclic AMP / Q000096:biosynthesis; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D051381:Rats; D013268:Stimulation, Chemical; D013997:Time Factors
chemical_list: D006165:Guanylyl Imidodiphosphate; D008345:Manganese; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D008274:Magnesium; D007545:Isoproterenol; D002118:Calcium