Corticotropin stimulates cyclic nucleotide independent protein kinase activity of intact adrenocortical cells

Abstract

Intact adrenocortical cells possess cyclic nucleotide-independent protein kinase activity which is capable of phosphorylating endogenous proteins and casein when incubated in the presence of [γ -³²P]ATP. The cyclic nucleotide-independent enzyme was dependent on cell number and temperature and had an apparent K_m for ATP of 6.5×10⁻⁵M and a V_max of 12.5 pmol/3 min/2×10⁵ cells at 37°C. Phosphorylation of endogenous proteins by this kinase was increased by treatment of intact cells with corticotropin (2.2 nM) for 24 h. In control cells, two endogenous proteins of apparent molecular weights of 39,000 and 76,000 were phosphorylated. In corticotropin-treated cells, another protein of apparent molecular weight of 87,000 was also phosphorylated. Thus, this protein kinase activity, which appears to be located on the plasma membrane, may be involved in mediating longer term actions of corticotropin on the adrenal cortex.