Protein phosphorylation in a dopamine-sensitive homogenate of rat caudate. Effect of adenosine 3',5'-cyclic monophosphate and putative neurotransmitters.

Adenosine 3′,5′-cyclic monophosphate (cyclic AMP) and its 8-methylthio derivative stimulate the incorporation of 32P into proteins endogenous to a homogenate of rat caudate nucleus when 4 μM [γ−32P] ATP is usedas substrate. Higher concentrations of ATP reduced the effect of the cyclic nucleotide until at 400 μM no significant increase in protein phosphorylation was seen. Incubation of the homogenate with 400 μM ATP and 100 μM dopamine resulted in an approx. 2-fold increase in cyclic AMP but did not alter caudate protein phosphorylation suggesting that the catecholamine could not stimulate protein phosphorylation under the experimental conditions used in the present study.