[Isolation and study of the properties of the catalytic subunit of cAMP-dependent protein kinase of the small intestinal mucosa of the rabbit]

cAMP-dependent and casein proteinkinase were found in cytosol of the rabbit small intestine mucosa. cAMP-dependent proteinkinase of cytosol is represented by two forms of types I and II. The activity of enzymes of types I and II constitutes 10 and 90%, respectively. Casein proteinkinase is represented by a single form. The catalytic subunit of cAMP-dependent proteinkinase of type II was isolated in a homogenous state. The catalytic subunit phosphorylates histones H1, H2a, H2b and protamine and to a far less degree histones H3, H4 and casein (H2b greater than H1 greater than H2a greater than protamine much greater than H3 greater than casein). The Km value for histone H1 is equal to 65 mkM, and that for Mg-ATP 12 mkM. Chloromethylpyrophosphonate and adenosine p-fluorosulfobenzoate were studied as affine modifiers of the active center of the catalytic subunit from the small intestine mucosa. It was shown that only adenosine p-fluorosulfonate is an irreversible inhibitor of the catalytic subunit.