Ca2+ and cyclic AMP regulate phosphorylation of same two membrane-associated proteins specific to nerve tissue.

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Abstract
It was previously shown that addition of cyclic(c)AMP to a synaptic membrane fraction incubated with [.gamma.-32P]ATP stimulated the phosphorylation of 2 proteins, designated proteins Ia and Ib, found only in nerve tissue. Addition of Ca2+ plus veratridine to [rat cerebral cortex] synaptosomes preincubated with 32P (inorganic phosphous) stimulated the phosphorylation of 2 proteins with similar apparent MW. Various techniques have now been used to determine whether the 2 proteins phosphorylated in synaptosomes in the presence of Ca2+ plus veratridine are the same as proteins Ia and Ib phosphorylated in synaptic membranes in the presence of cAMP. The proteins phosphorylated by the 2 procedures were extracted under similar conditions, had similar apparent MW and charges, and were digested by collagenase at similar rates and to the same radioactive intermediates and end products. The 2 sets of proteins were digested by 3 other proteolytic enzymes to phosphopeptides with similar molecular weights. Ca2+ and cAMP are each capable of regulating the phosphorylation of proteins Ia and Ib.