Isolation and purification of a new 105 kDa protein kinase from rat liver nuclei

A protein kinase was purified from rat liver nuclei by affinity chromatography on poly(L-lysine)-agarose and protein kinase inhibitor-Sepharose 4B columns. The relative molecular weight of this protein kinase is 105000 (determined by 10% SDS-polyacrylamide slab gel electrophoresis, gel filtration on Sephadex G-200 and sedimentation velocity ultracentrifugation). Its pH optimum is between 8.0 and 9.0. It is active over a wide range of mg2+ concentrations, and its activity is stimulated by several small acidic proteins (calmodulin, lactalbumin, parvalbumin, protein kinase inhibitor and troponin C). The enzyme phosphorylates a variety of substrates including casein, histones, protamine and the synthetic basic polypeptides, poly(L-arginine) and poly(L-lysine).