Inhibition by diuretics of cyclic 3′,5′‐AMP‐dependent protein kinase from toad bladder epithelium

Abstract

1 A cAMP-dependent protein kinase enzyme has been isolated from toad bladder epithelium. 2 This enzyme catalyses the phosphorylation of histones; a reaction stimulated by 0·1 μm cAMP. 3 Activity of this enzyme in the presence of 01 μm cAMP was significantly inhibited by 100 μm mercuderamide, bumetanide and frusemide. A small, though statistically insignificant inhibition was seen with the same concentrations of hydrochlorothiazide and ethacrynic acid. 4 The half maximal inhibition was achieved with mercuderamide, 5 μm, and with frusemide and bumetanide 600 μm.