ACTH, cyclic nucleotides, and brain protein phosphorylation in vitro.

Endogenous phosphorylation of proteins from rat brain synaptosomal plasma membranes was studied in vitro. Cyclic AMP (cAMP) markedly stimulated(32)P incorporation in three protein bands with molecular weights of 75,000, 57,000, and 54,000, respectively. The effect of the behaviorally active peptide ACTH1-24 on this endogenous phosphorylation in vitro was studied using peptide concentrations from 10(-10) to 10(-4) M. In a number of protein bands, a biphasic effect of ACTH1-24 was observed: in concentrations of 10(-4)-10(-5) M, a reduced amount of(32)P was found; in concentrations of 10(-6)-10(-7) M, hardly any effect could be detected, whereas consistently at concentrations around 10(-8) M, a significant decrease was again observed. The phosphoprotein bands affected by in vitro addition of ACTH1-24 were of a smaller molecular weight than those affected by in vitro addition of cAMP.