MECHANISM OF THE INHIBITION OF HOG GASTRIC H-ATPASE BY THE SELENOORGANIC COMPOUND EBSELEN(, K+)

The effect of 2-phenyl-1,2-benziselenazol-3 (2H)-one (ebselen, CAS 609 40-34-3), a seleno-organic compound, on the partial reaction steps of H+, K+-ATPase in hog leaky gastric vesicles was examined. Ebselen inhi bited K+-dependent ATPase activity (IC50 = 0.06 mu mol/l), phosphoenzy me formation (IC50 mu mol/l), and K+-dependent p-nitrophenylphosphatas e activity (IC50 = 0.09 mu mol/l: dephosphorylation step of this enzym e). Furthermore, this compound prevented changes in the fluorescence i ntensity of flourescein isothiocyanate-labeled enzyme (E(1) --> E(2)K form IC(5)0 = 0.33 mu mol/l). Pretreatment with 2 mmol/l of dithiothre itol (DTT) used as a sulfhydryl compound completely protected against these inhibitory effects. These findings indicate that ebselen-induced inactivation of gastric H+, K+-ATPase may result from prevention of t he partial reaction steps, which include phosphorylation, dephosphoryl ation and conformational change (E(1) --> E(2)K form), through interfe rence with sulfhydryl groups of the enzyme.