Purification and Characterization of Two Cyclic AMP-Independent Protein Kinases from AH-66 Hepatoma Ascites Cells1

Abstract

Casein kinase 1 (CK 1) and casein kinase 2 (CK 2) were purified from the cytosol fraction of AH-66 cells to electrophoretic homogeneity by a simple procedure based on our finding that CK 1 and CK 2 are chromatographically distinct on phosvitin-Sepharose. The amino acid composition of CK 2 resembles those of cyclic AMP-dependent and cyclic GMP-dependent protein kinases but is considerably different from that of CK 1. Both CK 1 and CK 2 were markedly stimulated by low concentrations of spermine and spermidine but were practically unaffected by putrescine. When CK 1 and CK 2 were added back to AH-66 cytosol, they promoted the phosphorylation of the same cytosolic proteins that were phosphorylated endogenously. Although most of the cytosolic proteins phosphorylated by CK 1 and CK 2 were common, some proteins were preferentially phosphorylated by either CK 1 or CK 2. Interestingly, CK 1 was able to phosphorylate the plasma membrane proteins of AH-66 cells. In contrast, enhancement of the phosphorylation of the membrane proteins by CK 2 was practically undetectable.