[Comparative characteristics of membrane-bound and solubilized 3':5'-AMP-dependent protein kinase from myocardium...

A kinetic study of membrane-bound and solubilized 3' : 5'-AMP-dependent protein kinase from rabbit myocardium sarcoplasmic reticulum membranes was carried out. Both enzyme preparations catalyzed the phosphorylation of exogenous protein substrates (histones) and endogenous membrane substrate. Solubilization of protein kinase and its subsequent purification on columns with DEAE-cellulose and hydroxyapatite did not change the substrate specificity and kinetic properties of the enzyme. Both preparations differed in the maximal rates of the reaction; the differences in apparent Km values for ATP and histone H1 were insignificant. The membrane-bound and solubilized preparations had the same pH optimum of 6,5. Their maximum activity was exerted at Mg2+ concentration considerably exceeding that of ATP. Ca2+ at micromolar concentrations had no effect on the enzyme activity.