title: Inhibition of urease by bismuth(III): implications for the mechanism of action of bismuth drugs.
abstract: Bismuth compounds are widely used for the treatment of peptic ulcers and Helicobacter pylori infections. It has been suggested that enzyme inhibition plays an important role in the antibacterial activity of bismuth towards this bacterium. Urease, an enzyme that converts urea into ammonia and carbonic acid, is crucial for colonization of the acidic environment of the stomach by H. pylori. Here, we show that three bismuth complexes exhibit distinct mechanisms of urease inhibition, with some differences dependent on the source of the enzyme. Bi(EDTA) and Bi(Cys)(3) are competitive inhibitors of jack bean urease with K(i) values of 1.74 +/- 0.14 and 1.84 +/- 0.15 mM, while the anti-ulcer drug, ranitidine bismuth citrate (RBC) is a non-competitive inhibitor with a K (i) value of 1.17 +/- 0.09 mM. A (13)C NMR study showed that Bi(Cys)(3) reacts with jack bean urease during a 30 min incubation, releasing free cysteines from the metal complex. Upon incubation with Bi(EDTA) and RBC, the number of accessible cysteine residues in the homohexameric plant enzyme decreased by 5.80 +/- 0.17 and 11.94 +/- 0.13, respectively, after 3 h of reaction with dithiobis(2-nitrobenzoic acid). Kinetic analysis showed that Bi(EDTA) is both a competitive inhibitor and a time-dependent inactivator of the recombinant Klebsiella aerogenes urease. The active C319A mutant of the bacterial enzyme displays a significantly reduced sensitivity toward inactivation by Bi(EDTA) compared with the wild-type enzyme, consistent with binding of Bi(3+) to the active site cysteine (Cys(319)) as the mechanism of enzyme inactivation.
authors.affiliation: Department of Chemistry and Open Laboratory of Chemical Biology, The University of Hong Kong, Pokfulam, Hong Kong, PR China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Scott B
authors.initials: SB
authors.lastname: Mulrooney
authors.forename: Andy F K
authors.initials: AF
authors.lastname: Leung
authors.forename: Yibo
authors.initials: Y
authors.lastname: Zeng
authors.forename: Ben B C
authors.initials: BB
authors.lastname: Ko
authors.forename: Robert P
authors.initials: RP
authors.lastname: Hausinger
authors.forename: Hongzhe
authors.initials: H
authors.lastname: Sun
mesh_terms: D000595:Amino Acid Sequence; D000897:Anti-Ulcer Agents / Q000627:therapeutic use; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D001729:Bismuth / Q000737:chemistry / Q000378:metabolism* / Q000627:therapeutic use; D003545:Cysteine / Q000378:metabolism; D016481:Helicobacter Infections / Q000188:drug therapy; D007709:Klebsiella / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D016415:Sequence Alignment; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014510:Urease / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D000897:Anti-Ulcer Agents; D001426:Bacterial Proteins; D010940:Plant Proteins; D013438:Sulfhydryl Compounds; D014510:Urease; D003545:Cysteine; D001729:Bismuth