Purification of cytosolic cAMP-independent protein kinases from rat ventral prostate

1. 1. Two cAMP-independent protein kinases were purified from rat ventral-prostate and liver cytosol, and were designated PK-Cl and PK-C2 to distinguish them from the nuclear protein kinases described in the preceding paper. 2. 2. The yield of the prostate enzymes was about 5% each, and about 10% each for the liver enzymes. The average fold purification of the prostatic enzymes was 1892 and 3176 for protein kinase Cl and C2, respectively. Their average respective specific activity towards casein was 40,111 and 67,340 nmol ³²P incorporated/hr per mg of enzyme protein. 3. 3. protein kinase Cl comprised one polypeptide of M_r 39,000 which underwent phosphorylation in the presence of Mg²⁺ + ATP. Protein kinase C2 comprised three polypeptides of M_r 41,000; 38,000; 26,000. Of these only the M_r 26,000 polypeptide was autophosphorylated. 4. 4. The Mg²⁺ requirement for protein kinase Cl and C2 was between 1 and 4 mM depending on the nature of the protein substrate. Both enzymes were stimulated by 100-200 mM NaCl. 5. 5. K_m for ATP for Cl and C2 kinases was 0.01 mM; GTP could be used only by protein kinase C2 but with a markedly lower affinity. 6. 6. The enzymes were active towards casein, phosvitin, dephosphophosvitin, and spermine-binding protein in vitro, but demonstrated little activity towards histones. 7. 7. Despite several similarities in these general properties of cytosolic protein kinases Cl and C2 with those of nuclear protein kinases N1 and N2, a number of difference are also noted.