Further characterization of a protein kinase-substrate complex precipitable with Ca2+ from the cytosol fraction of AH-66 hepatoma cells.

The properties of a protein kinase-substrate complex precipitated with Ca2+ from the cytosol of AH-66 hepatoma cells were characterized. The endogenous phosphorylation reaction of the complex was little affected by addition of histone, cyclic nucleotides, Ca2+-calmodulin, or Ca2+-phospholipid but was increased about two-fold by addition of casein. The complex contained several phosphate acceptor proteins with molecular weights ranging from 74,000 to 13,000 as analyzed by two-dimensional gel electrophoresis. These phosphate acceptor proteins were specifically concentrated in the complex. The protein kinase in the complex was purified by successive chromatography and proved to be casein kinase 2.