Calcium- and cyclic AMP-regulated protein kinases of bovine central-nervous-system myelin

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Abstract
Bovine CNS myelin contained both Ca2+-activated and cAMP-dependent protein kinases. Each enzyme possesses unique solubility and substrate-specificity characteristics. The Ca2+-activated enzyme, like its substrate (basic protein), is probably deeply embedded in the neural membrane, whereas the cAMP-dependent kinase appears to be much less tightly associated with myelin. Treatment of insoluble myelin fraction housing the Ca2+-activated kinase with phospholipase A2 and phospholipases A2 + C causes a decrease in its ability to become activated by Ca2+. This can be countered by phosphatidylserine and phosphatidylethanolamine. Whereas the activity of the Ca2+-activated membrane-associated kinase is inhibited by chlorpromazine, dibucaine, melittin and Triton X-100, it is activated by certain phorbol diesters (4.beta.-phorbol 12-myristate 13-acetate, 4.beta.-phorbol 12,13-didecanoate, 4.beta.-phorbol 12,13-dibenzoate and 4.beta.-phorbol 12,13-diacetate), which appear to exert this effect by lowering the concentration of Ca2+ normally required for the activation of this enzyme. The activation of the membrane-associated kinase by Ca2+ most probably requires certain lipids, perhaps those already present in the membrane.