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 β-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 β-agonist, is very potent in reversing the Gpp(NH)p permanently active state to the basal state. β-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.