Endogenous phosphorylation of four cerebral cortical membrane proteins: Role of cyclic nucleotides, ATP and divalent cations

Endogenous phosphorylation of 4 membrane-bound protein components of cerebral cortex was studied in vitro. Cyclic AMP was shown to stimulate phosphorylation to a major extent in protein components designated D, E and G, but to a minor extent in protein component F. The time course of phosphorylation of each of these components is affected differently by (a) the presence of cyclic nucleotides or zinc ions and (b) the concentration of ATP and magnesium ions in the reaction mixture. Although a different membrane preparation was used here than by Ueda et al.²⁹, molecular weight determination and response to divalent cations, magnesium and zinc, suggest that components D and E may be the same as their proteins I and II. The newly described phosphoproteins, F and G, are respectively the least and most stimulated by the addition of cyclic AMP. Under certain conditions phosphate content in protein E can be increased by cyclic AMP and decreased by cyclic GMP.