Interaction of a casein kinase (G-TYPE) with a specific endogenous inhibitor: Possible target for the regulation of a cyclic nucleotide-independent protein kinase activity by polyamines

Abstract

Cyclic l~ucleotide-independent ATP:protein phosphotransferase (protein kinases, PK) activities have been described in mammalian tissues [ 11. Criteria for their characterization have been established [2] and highly purified preparations have been obtained by several research groups f3-71. Although these PK have been suggested to be involved in the modulation of key metabolic pathways [S-lo], possible regulation and intracellular effecters of their activity remain to be defined. We have reported the characterization in bovine adrenal cortex of a soluble cyclic nucleotide-independent casein kinase (CK) activity [ 111. This activity has subsequently been shown to represent several enzymatic moieties which could be classified into two groups according to their properties [ 12,131: a type A casein kinase (CKA) using only ATP and a type G (CKG) using GTP as well as ATP as phosphoryl donor. It was then found that an endogenous inhibitory factor, specifically directed toward CKG activity (CKG I) was present in the same tissue. The inhibitor was isolated and characterized as a heat-stable protein moiety [ 141. The presence of CKG I led to a mostly inhibited CKG activity in crude adrenal cortex cytosol, suggesting that a CKG-CKG I interaction might represent a potential regulatory pathway of CKG activity in intact cell [ 141. Here we report the observation that several naturally occuring polyamine structures can reverse