[Study by the spin-label method of relaxation properties of protein kinase, its subunits and the catalytic...

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.