Rat liver plasma membranes contain a lipid‐dependent protein kinase activity

Abstract

The treatment of rat liver plasma membranes with EDTA resulted in substantial release of a protein kinase activity. Using histones as external substrates both phosphatidylserine (PS) and diolein activated the enzyme. The activatory effect of PS but not that of diolein depended on Ca²⁺. In contrast, the enzyme activity was inhibited by both PS and diolein when the substrate was protamine. The inhibition by PS, unlike by diolein, depended on Ca²⁺. Data suggest that mobilization of plasma membrane-bound Ca²⁺ by physiological stimuli may be accompanied by release of the lipid-dependent protein kinase into the cytoplasm.