Mechanism of Anti-urease Action by the Anti-ulcer Drug Ecabet Sodium

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To investigate the mechanism of the anti-urease action of ecabet sodium (ecabet) observed in Helicobacter pylori in vitro, the effects of ecabet on purified urease from jack bean were studied in comparison with the effects of the specific urease inhibitor benzohydroxamic acid (BHA). After incubation of the enzyme with the test drug for a period of time, urease activity was measured. Ecabet depressed the activity below pH 5, and the lower the pH, the greater the degree of depression. The degree of depression by ecabet increased gradually during incubation and reached a plateau in 20 min, whereas that by BHA attained a maximum rapidly. The IC₅₀ values of ecabet and BHA were 2.1 mg/ml and 0.5 μg/ml, respectively. When the incubation mixture of urease with an inhibitor was diluted and further incubated, the depressed activity by BHA reverted gradually, but that by ecabet did not. When the incubation mixture of urease with ecabet was centrifuged, the urease activity of the mixture decreased in parallel with the reduction in protein concentration of the supernatant. When the incubation mixture of urease and ¹⁴C-ecabet was ultrafiltered to remove the drug, the radioactivity in the retentate remained in parallel with the degree of reduction of urease activity of jack bean, and suggest that the depression is caused by irreversible binding of ecabet to urease followed by denaturation of the enzyme protein.