Widespread Occurence of Calcium-Activated, Phospholipid Dependent Protein Kinase in Mammalian Tissues1

Abstract

Ca²⁺-activated, phospholipid-dependent multifunctional protein kinase originally found in rat brain occurs in a variety of mammalian tissues. In most tissues the enzyme activity is comparable to that of cyclic AMP-dependent protein kinase when assayed with calf thymus H1 histone as phosphate acceptor. In some tissues such as platelets, brain, and lymphocytes the enzyme far exceeds the cyclic AMP-dependent enzyme. This species of protein kinase found in various tissues shows very similar physical, kinetic, and catalytic properties, and does not appear to show tissue and species specificities. It is conceivable that this protein kinase plays roles in transmembrane control of protein phosphorylation by a large number of extracellular messengers which induce phosphatidylinositol turnover in their target tissues.