GUANOSINE 3' - 5' MONOPHOSPHATE-DEPENDENT PROTEIN-KINASE FROM BOVINE ADRENAL-CORTEX - PARTIAL-PURIFICATION AND CHARACTERIZATION

Cyclic GMP-dependent protein kinase has been partially purified from bovine adrenal cortex. The enzyme was specifically activated by cyclic GMP at lower concentrations. The Ka for cyclic GMP was 9 × 10-8 M whereas that for cyclic AMP was 7 × 10-6 M. An optimum concentration of 75 mM magnesium was needed for maximal stimulation by cyclic GMP whereas 10 mM magnesium ion concentration was found to be optimal for the cyclic AMP-dependent protein kinase. The enzyme was found to have a molecular weight of 225,000 based on gel filtration. When the enzyme was photoaffinity labeled with cyclic GMP, it again demonstrated the molecular weight of 225,000. This indicated that the enzyme was not dissociated into regulatory and catalytic components by cyclic GMP. The protein was composed of two polypeptides having the same molecular weight of 110,000 as shown by SDS-PAGE, and thus it appears to consist of two subunits of equal size. This study thus provides the direct evidence for the presence of cyclic GMP-dependent protein kinase in adrenal cortex and lends additional support for the molecular model proposed earlier from our laboratory postulating a crucial role for this protein in adrenal steriodogenesis [4]. © 1979.