A heparin-sensitive nuclear protein kinase. Purification, properties, and increased activity in rat hepatoma relative...

A cyclic-nucleotide independent heparin-sensitive nuclear protein kinase (NII) from the Morris hepatoma 3924A has been purified by a combination of ion exchange and affinity chromatographic procedures and velocity gradient centrifugation. The purified kinase had a molecular weight of 140,000 as determined by gel filtration. Two polypeptides (Mr = 42,000 and 25,600) were present in the purified preparation in approximately equimolar concentrations. The protein kinase employed Mg2+ and Co2+ as divalent ion and preferred the nonhistone proteins, casein or phosvitin, as protein acceptors. In the presence of Mg2+, it utilized both ATP and GTP as substrates and transferred the terminal nucleotide phosphate to serine and threonine residues of the protein acceptor. Phosphorylation of casein was stimulated by polyamines, particularly spermine. This polyamine preferentially enhanced phosphate transfer to threonine. The enzyme was inhibited by several compounds including heparin, the o-n-octyloxime of rifamycin (AF/013), 3'-dATP, o-phenanthroline, polynucleotides, and ADP. Of these inhibitors, heparin was the most potent and completely abolished kinase activity at a concentration of 0.1 micrograms/ml. The kinase could be autophosphorylated by incubation with Mg2+ and [gamma-32P]ATP; under these conditions phosphorylation was confined to the polypeptide of Mr = 24,600 and was completely inhibited by heparin. Based on the unique properties of NII protein kinase (ability to use GTP, stimulation by spermine, sensitivity to heparin), a selective assay was developed which could measure NII activity in the presence of other nuclear kinases. Under the optimal assay conditions, the nuclear extract of hepatoma 3924A was found to contain at least five times more NII kinase activity than that of normal adult liver. Analysis of extensively purified preparations from the two sources confirmed these results. After purification 11 times more NII protein kinase activity was obtained from hepatoma 3924A than from liver. Although hepatoma and liver protein kinases exhibited many common properties, they displayed distinct nucleotide saturation kinetics. The apparent Km for ATP was 10 microM for hepatoma protein kinase and 24 microM for the liver enzyme.