Inactivation of jack bean urease by scutellarin: Elucidation of inhibitory efficacy, kinetics and mechanism

In the present study, the inactivation effect of scutellarin (SL) on jack bean urease was investigated to elucidate the inhibitory potency, kinetics and mechanism of inhibition. It was revealed that SL acted as a concentration- and time-dependent inactivator of urease characteristic of slow-binding inhibition with an IC50 of 1.35 +/- 0.15 mM. The rapid formation of the initial SL-urease complex with an inhibition constant of K-i = 5.37 x 10(-2) mM was followed by a slow isomerization into the final complex with the overall inhibition constant of K-i* = 3.49 x 10(-3) mM. High effectiveness of thiol protectors, such as L-cysteine (L-cys), 2-mercaptoethanol (2-ME) and dithiothreitol (DTT) significantly slowed down the rate of inactivation, indicating the strategic role of the active site sulfhydryl group in the blocking process. While the insignificant protection by boric acid and fluoride from the inactivation further confirmed that the active site cysteine should be obligatory for urease inhibition, which was also rationalized by the molecular docking study. The inhibition of SL on urease proved to be reversible since SL-blocked urease could be reactivated by DTT application and multidilution. The results obtained indicated that urease inactivation resulted from the reaction between SL and the sulfhydryl group. (C) 2013 Published by Elsevier B.V.