[Binding of a holoenzyme and cAMP-dependent protein kinase subunits with cell nuclei]

The interaction of cAMP-dependent protein kinase from porcine brain with nuclei isolated from the same source was studied. The shape of the curves for the holoenzyme and subunit binding to the nuclei points to the specificity of this interaction and allows for the calculation of the number of protein binding sites. An extremely low degree of binding of the regulatory subunit phosphoform to the nucleus was demonstrated. It was shown that in the nuclei the regulatory subunit binds to proteins whose molecular mass varies from 15,000 and 55,000 Da. Proteolytic fragments of the regulatory subunit do not interact with chromatin proteins; in the nuclei they are functionally inactive and are not involved in protein-protein interactions.