A study of the inhibition of jack bean urease by garlic extract

An inhibiting effect of fresh garlic extract (GE) on jack bean urease has been investigated in order to elucidate the kinetics and mechanism of inhibition. The system: jack bean urease-garlic extract-urea, can be treated as a model system in the studies on the utility of garlic in the therapy of diseases caused by Helicobacter pylori and other bacteria producing urease. The influence of fresh aqueous garlic extract on the activity of jack bean urease at 22 °C in 20 mM phosphate buffer, pH 7 was investigated. The loss of urease activity was found to be directly proportional to alk(en)yl thiosulfinates (TS) content in the garlic extract. The inhibitory activity of GE was compared with the activity of synthetic allicin. The results indicate that the inhibition of urease by GE is irreversible and incubation time-dependent. The kinetics of the inhibition was found to be biphasic; each phase obeyed first-order kinetics. Thiol reagents (L-cysteine, 2-mercaptoethanol, glutathione, dithiothreithol) strongly protect the enzyme from the loss of enzymatic activity, while urea and boric acid show weaker protection. GE-modified urease could be reactivated with dithiothreitol. This study demonstrates, that the inhibition of urease by GE should be atrributed to the reaction of TS with the SH-group (Cys592) found in the active site of urease.