Selective effects of an essential sulfhydryl group on the activation of dopamine- and guanine nucleotide-sensitive adenylate cyclase.

Treatment of membranes from the dog caudate nucleus with sulfhydryl alkylating agents, N-ethylmaleimide and p-chloromercuribenzoate, results in selective inhibition of dopamine-sensitive adenylate cyclase activity that can be distinguished from effects on basal enzyme activity. Fifty per cent inhibition of dopamine-sensitive adenylate cyclase activity was observed in the presence of 10(-5) M N-ethylmaleimide and 3 X 10(-6) M p-chloromercuribenzoate. N-Ethylmaleimide (10(-5) M or less) also inhibited GTP- and NaF-stimulated adenylate cyclase activity, but had no effect on basal adenylate cyclase activity (assayed in the presence of magnesium) and on enzyme activity assayed in the presence of manganese. The reducing agents dithiothreitol, 2-mercaptoethanol, glutathione, and cysteine had no inhibitory effect on dopamine-sensitive adenylate cyclase activity. Pretreatment of membranes with guanyl-5'-yl imidodiphosphate or guanosine 5'-O-(3-thio)triphosphate prior to incubation with N-ethylmaleimide prevented the inhibitory effect of N-ethylmaleimide on adenylate cyclase activity. The results suggest that a reactive sulfhydryl group in the domain of the GTP-binding protein is important for the coupling of the components of the dopamine-sensitive adenylate cyclase complex in brain.