Multiple forms of protein kinase in liver cell: II - Nuclear kinases and cytosol phosvitin kinase

Abstract

Summary Two protein kinase peaks have been resolved from rat liver nuclear non histone proteins on DEAE cellulose column. One of the peaks, kinase I, is active on casein and the other peak, kinase II, is active on casein and phosvitin. Kinase I was resolved into 2 active peaks by polyacrylamide gel electrophoresis. Kinase II was resolved into 3 peaks, all active on both phosvitin and casein. Optimal pH and Mg ++ concentration were determined. NaCl activated phosvitin phosphorylation and inhibited casein phosphorylation. PHMB inhibited kinase I more than kinase II. Preincubation at 37° had little effect on casein phosphorylation by kinase II, but partly inactivated kinase I and the phosphorylation of phosvitin by kinase II. These results are compatible with the existence of 2 kinases, one active on casein, the other containing two sites, one active with casein, the other active with phosvitin. A kinase was purified from liver cytosol which is active on casein and on phosvitin. It is similar in most respects to nuclear kinase II. NHP contains a histone kinase which is very unstable and which is different from the cytosol histone kinases previously described. None of these kinases are activated by cyclic AMP.