Mechanism of the inhibition of hog gastric H+,K(+)-ATPase by the seleno-organic compound ebselen.

The effect of 2-phenyl-1,2-benzisoselenazol-3 (2H)-one (ebselen, CAS 60940-34-3), a seleno-organic compound, on the partial reaction steps of H+,K(+)-ATPase in hog leaky gastric vesicles was examined. Ebselen inhibited K(+)-dependent ATPase activity (IC50 = 0.06 mumol/l), phosphoenzyme formation (IC50 = 0.25 mumol/l), and K(+)-dependent p-nitrophenylphosphatase activity (IC50 = 0.09 mumol/l: dephosphorylation step of this enzyme). Furthermore, this compound prevented changes in the fluorescence intensity of flourescein isothiocyanate-labeled enzyme (E1-->E2K form, IC50 = 0.33 mumol/l). Pretreatment with 2 mmol/l of dithiothreitol (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 the partial reaction steps, which include phosphorylation, dephosphorylation and conformational change (E1-->E2K form), through interference with sulfhydryl groups of the enzyme.