Partial purification and characterization of a novel bovine adrenocortical protein kinase that phosphorylates endogenous 120,000 dalton peptide

Abstract

We describe partial purification of a novel protein kinase (designated PK 380) from bovine adrenal cortex. The enzyme binds neither cyclic AMP or cyclic GMP, nor phosphorylates the known exogenous substrates such as histones, phosphorylase b, casein, phosvitin, or protamine, in the presence or absence of the cyclic nucleotides. The protein kinase activity of the enzyme was not inhibited by the cyclic AMP-dependent protein kinase inhibitor. Addition of exogenous calcium, calmodulin, or EGTA did not affect the process of phosphorylation. It catalyzes, however, the phosphorylation of an endogenous 120,000 dalton polypeptide. We, therefore, conclude that PK 380 is a cyclic nucleotide- and calcium-or calcium-calmodulin independent protein kinase, that phosphorylates the endogenous substrate, a 120,000 dalton polypeptide. Recently, we have found that PK 380 specifically phosphorylates eukaryotic initiation factor 2 α. This enzyme therefore, might play an important role in the translation control of eukaryotic cell.