Activation of Myelin Protein Kinase by Diacylglycerol and 4β-Phorbol 12-Myristate 13-Acetate

In an effort to gain a more complete understanding of the regulation of myelin basic protein phosphorylation, we have been interested in defining further the mode of regulation of the myelin protein kinase involved in this posttranslational modification. Here we report the partial purification of a protein kinase from rat brain myelin. By gel filtration, it was determined that the molecular weight of this enzyme was in the range of 70-80 X 10(3) daltons Furthermore, it was established that at low calcium concentrations, this enzyme was markedly activated by phosphatidylserine in combination with either 4 beta-phorbol 12-myristate 13-acetate or diolein. The enzyme was not affected by cyclic AMP or by calcium, alone or in combination with calmodulin. On the basis of these findings this enzyme can be identified as a protein kinase C-like enzyme.