A selective inhibitor of cAMP-dependent protein kinase isolated from an alkalophilic strain of Bacillus species

Abstract

Many alkalophilic bacteria were found to produce inhibitors of protein kinases. We isolated a novel inhibitor of protein kinase from an alkalophilic strain of Bacillus species. This substance was A heat-stable peptide with a molecular weight of 13, 000 daltons. It was found to be a selective inhibitor of cyclic AMP-dependent protein kinase (A kinase). The inhibition of a kinase by this substance was non-competitive with histone or ATP. It behaved distinctly; other known inhibitors such as H-7, H-8, Staurosprine, K-252 and Erbstatine inhibit protein kinase less selectively and their functions are competitive with either substrate or ATP. This inhibitor was found to bind to the regulatory subunits of A kinase and markedly inhibited the separation of the catalitic subunits from A kinase induced by the binding of cAMP despite of no effect on the binding of cAMP. Thus, the activation step of A kinase was influenced by this inhibitor. This molecule had no effect on the inhibition by cAMP of CHO cell proliferation. This may have been due to the inability of this molecule to reach the target in the cell. Modification of the molecule itself or the administration method is needed for cellular or animal application.