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By the method of chemical modification the active site of cAMP-dependent pig brain protein kinase was shown to contain a carboxyl group. The kinetic parameters of irreversible inhibition of the enzyme by water-soluble carbodiimide in the presence of ethyl ester of glycine were determined. The ionized carboxyl group-containing amino acid residue found is evidently localized in the immediate proximity to the reaction center. The comparison of the reaction rates of phosphate transfer from the intermediate phosphoform of the enzyme under native and denatured conditions suggests that this residue acts as the general base catalyst of this process.

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.

The reaction of the solvolysis of the phosphointermediate, formed in the course of the phosphotransferase reaction was studied using a number of non-specific nucleophilic agents. The methods of identification of the solvolysis products and determination of kinetic parameters were developed. The estimated dependence of the reaction of the reactivity of the nucleophilic agents versus their basicity allowed some conclusions about the transition state structure in the cases of enzyme's interaction with nucleophilic agents and protein substrate. The energy contribution of the specific interaction of the enzyme with histone H1 was evaluated.

Using the spin label method, the rotational relaxation in solution of adenosine 3',5'-monophosphate-dependent protein kinase and its subunits as well as the complexes of the enzyme with the substrate, histone H1, was studied. The rotational correlation time of the spin labeled macromolecules was measured on the basis of the quantitative estimation of the label mobility in relation to the protein globule. The holoenzyme molecule was found to be a rigid sphere. Whereas the complex of the globular catalytic subunit of the enzyme with a specific protein substrate, the spin labeled histone H1, appeared a flexible formation. The relaxation properties of the histone H1 molecule selectively labeled by the spin label in its globular part were investigated.