The time course of the phosphorylation of proteins in the synaptic plasma membrane and the effect of certain cations.

The phosphorylation of proteins in the synaptic plasma membrane is a rather slow reaction taking several minutes to saturate all the phosphate acceptor sites. (The time for half the protein bound phosphate groups to turnover is about 1 min). A divalent cation is needed as a cofactor for the reaction. At high (0.5 mM) ATP concentrations Mg2+ is more effective than Mn2+ but at low (10 microM) ATP concentrations the reverse is the case. Zn2+ and Ca2+ support very little phosphorylation.