An endogenous, Mg2+-dependent, protein kinase in coated vesicles from synaptosomes of bovine brain

Abstract

Coated vesicles (CV) extracted from bovine brain synaptosomes were purified by differential and continuous sucrose density gradient centrifugation. An endogenous protein kinase, dependent upon Mg2+, was found in the vesicles. The kinase catalysed, independently of cyclic nucleotides and Ca2+ plus calmodulin, the incorpotation of the radioactive phosphate of [γ-32p]-ATP and -GTP into a protein, 48,000 in molecular weight, termed C-48. The CV-protein kinase mediated the phosphorylation of Phosvitin, but poorly that of casein, histone, or protamine. The enzyme activity was inhibited by heparin sulfate, an inhibitor in the receptor-mediated endocytosis in fibroblasts in culture. Spermidine slightly suppressed the activity of the kinase. The results showed that the endogenous protein kinase in CV from brain synaptosomes, inhibited by heparin sulfate, agreed in many respects with the Phosvitin kinase reported to be distributed in a variety of tisssues.