Rat adrenocortical carcinoma 494 autophosphorylating protein kinase, autophosphorylating protein kinase 500. Purification, biochemical and immunological characterization, and substrate specificity

A novel autophosphorylating protein kinase, autophosphorylating protein kinase 500, independent of cyclic AMP, cyclic GMP, calcium, and calmodulin was purified from rat adrenocortical carcinoma 494 by ammonium sulfate fractionation followed by the chromatographic steps of DEAE-cellulose, gel filtration, cyclic AMP-epoxy Sepharose, and phosphocellulose. Sometimes two additional chromatographic purification steps of chromatofocusing and gel filtration were necessary for complete purification. The enzyme was homogeneous as evidenced by one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sucrose density sedimentation studies indicated that Mr of the enzyme was 490,000, while ultracentrifugal analysis demonstrated a value of 481,400 (+/-7%). The protein was composed of two identical subunits each with Mr = 250,000. The enzyme molecule was slightly asymmetric with frictional and sedimentation coefficients of 1.28 and 18.20, respectively, and a Stokes radius of 66 A. Isoelectric focusing electrophoresis revealed a single peak with pI 4.6, indicating acidity of the protein. The enzyme self phosphorylated one or more of its serine residues. The reaction utilized the terminal phosphate of ATP; GTP was inactive. Divalent cations (5 mM Mn2+ or 10 mM Mg2+) were essential for optimum activity. Autophosphorylating protein kinase 500 did not phosphorylate the commonly used exogenous substrates such as histones, casein, phosvitin, or protamine. Analysis of autophosphorylating protein kinase 500 with rabbit anti-autophosphorylating protein kinase 500 IgG by immunoelectrophoresis and crossed immune electrophoresis demonstrated single arcs of precipitation, confirming the biochemical demonstration of enzyme purification and homogeneity. Indirect immunofluorescence studies revealed an intracytoplasmic localization of the enzyme in cultured and freshly isolated adrenocortical carcinoma 494 cells. Both cell types revealed an intensity of perinuclear enzyme fluorescence, but an absence of the enzyme in the nuclei or nucleoli. The anti-autophosphorylating protein kinase 500 IgG blocked the self-catalyzed phosphorylation of autophosphorylating protein kinase 500, providing immunological support of the biochemical results that autophosphorylation is an intrinsic characteristic of the enzyme. When autophosphorylating protein kinase 500 was incubated with membrane-bound ribosomes, it phosphorylated a Mr = 31,000 protein. This phosphorylation was blocked by the anti-autophosphorylating protein kinase 500 IgG.(ABSTRACT TRUNCATED AT 400 WORDS)