The interaction of Mn2+ with turkey erythrocyte adenylate cyclase

Mn2+ at concentrations below 0.1 mM supports the activation of turkey erythrocyte adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) by beta-agonists or NaF, similarly to Mg2+ at 5.0 mM. At higher concentrations, Mn2+ is strongly inhibitory, as is Mg2+ above 6 mM. Also, Mn2+ with GTP, but in the absence of beta-agonist, is very potent in reversing the Gpp(NH)p permanently active state to the basal state. beta-Receptor (R) to guanyl nucleotide regulatory protein (N) coupling still occurs at inhibitory Mn2+ concentrations, since the intrinsic kinetic parameters which characterize the R to N coupling interrelationship are unaffected by Mn2+ at a wide concentration range. It is suggested that the inhibitory effect of Mn2+ is due to the impairment of the guanyl nucleotide regulatory protein (N) to the catalytic subunit (C) interaction.