[Mechanism of action of cyclic AMP-dependent histone kinase. Substrate specificity of the catalytic enzyme unit].

Interaction of several nucleotide derivates with homogenous catalytic subunit of cyclo-AMP-dependent histone kinase from pig brain is studied. Inhibition constants of these compounds are calculated, and the affinity of inhibitors to the enzyme active site is evaluated. The nature of heterocyclic base is found to be the main contribution into binding with substrate. The enzyme specificity with respect to a number of bivalent metal ions is studied, and Mg2+ is demonstrated to be the only efficient enzyme activator. It is shown by means of stationary kinetics that histone kinase-catalysed phosphotransferase reaction has a "ping-pong"-like mechanism.