Urease is a metalloenzyme that catalyzes the hydrolysis of urea into ammonia and carbon dioxide, which has a negative impact on human health and agriculture. In this study, the inactivation of jack bean urease by nitidine chloride (NC) was investigated to elucidate the inhibitory effect, kinetics, and underlying mechanism of action. The results showed that NC acted as a concentration- and time-dependent inhibitor with an IC50 value of 33.2 ± 4.8 μM and exhibited a similar inhibitory effect to acetohydroxamic acid (IC50 = 31.7 ± 5.8 μM). Further kinetic analysis demonstrated that NC was a slow-binding and non-competitive inhibitor for urease. Thiol-blocking reagents (dithiothreitol, glutathione, and l-cysteine) significantly retarded urease inactivation, while Ni2+ competitive inhibitors (boric acid and sodium fluoride) synergetically suppressed urease with NC, suggesting that the active site sulfhydryl groups were possibly obligatory for NC blocking urease. Molecular docking simulation further argued its inhibition mechanism. Additionally, NC-induced deactivation of urease was verified to be reversible since the inactivated enzyme could be reactivated by glutathione. Taking together, NC was a non-competitive inhibitor targeting the thiol group at the active site of urease with characteristics of concentration dependence, reversibility, and slow binding, serving as a promising novel urease suppressant.
Keywords: alkaloids; enzyme kinetics; nitidine chloride; thiol group; urease inhibitor.