Cyclic adenosine 3',5'-monophosphate-dependent protein kinase of human erythrocyte membranes.

A cyclic AMP (adenosine 3’, 5’-monophosphate)-dependent protein kinase has been found in membranes derived from human erythrocytes which accounts for greater than 70% of the total cyclic AMP-dependent protein kinase activity of these cells. Components of the erythrocyte membranes were phosphorylated by membrane-bound protein kinase, but stimulation of the rate of phosphorylation by cyclic AMP was observed only when histones or protamine served as substrates. The membrane-associated cyclic AMP-dependent protein kinase resembles many soluble protein kinases; it requires 20 mu Mg2+ for maximal activity, has apparent K, values of 26 pg per ml and 8.3 pM for protamine and ATP, respectively, and a Ka for cyclic AMP of 28 nM. Erythrocyte membranes specifically bind cyclic AMP and exhibit a dissociation constant of 3.3 nM for the “membrane-cyclic AMP complex.” Cyclic AMP-independent protein kinase activity was dissociated from the membrane by treatment with 1 M NH&l, but the cyclic AMP-binding activity was retained by the particulate fraction. These findings suggest that the cyclic AMP-binding moiety is firmly integrated into the membrane structure, whereas the catalytic moiety may only be loosely associated with the membrane.