Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Urease obtained from seeds of Citrullus vulgaris fruits has been studied under three points of view: a) the effect of the urea analogs acetamide and hydroxi-urea on the enzyme kinetic b) the action of the sulfhydryl reagents and the reactivation agents on the enzyme c) the effect of X-rays and the protective action of the cysteamine. The Berthelot reaction for the determination of the liberated NH3 was used enzyme activity. Acetamide has no effect on urease kinetic. Hidroxy-urea which produces a typical green color when it is mixed with the Berthelot reagents at high concentrations, when properly diluted acts a aompetitive inhibitor of urease. Spectrophotometric experiments suggest that the studied urease decomposes hydroxi-urea with liberation of hydroxilamine. The sulphydril reagent, p-hydroxi-mercuribenzoate inhibits the enzime. Cysteine and dithiotreitol reactivate the enzyme activity in no more then 50% even when excess of the substances is used. Probably only in the first step of the urea hydrolysis, the enzyme behaves as a typical SH-enzyme. Urease is very sensitive to X-rays. Cysteamine acts as a protective agent of the enzyme. Dithiotreitol reinforces this protective action. This effect is clearly observed when the Fisbein catalytic method for urease is employed.
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PMID:[Studies on urease from the seeds of Citrullus vulgaris: action of chemical agents and ionizing radiations]. 103 92

We examined several compounds for their mechanisms of inhibition with the nickel-containing active site of homogeneous Klebsiella aerogenes urease. Thiolate anions competitively inhibit urease and directly interact with the metallocenter, as shown by the pH dependence of inhibition and by UV-visible absorbance spectroscopic studies. Cysteamine, which possesses a cationic beta-amino group, exhibited a high affinity for urease (Ki = 5 microM), whereas thiolates containing anionic carboxyl groups were uniformly poor inhibitors. Phosphate monoanion competitively inhibits a protonated form of urease with a pKa of less than 5. Both the thiolate and phosphate inhibition results are consistent with charge repulsion by an anionic group in the urease active site. Acetohydroxamic acid (AHA) was shown to be a slow-binding competitive inhibitor of urease. This compound forms an initial E.AHA complex which then undergoes a slow transformation to yield an E.AHA* complex; the overall dissociation constant of AHA is 2.6 microM. Phenylphosphorodiamidate, also shown to be a slow-binding competitive inhibitor, possesses an overall dissociation constant of 94 pM. The tight binding of phenylphosphorodiamidate was exploited to demonstrate the presence of two active sites per enzyme molecule. Urease contains 4 mol of nickel/mol enzyme, hence there are two nickel ions/catalytic unit. Each of the two slow-binding inhibitors are proposed to form complexes in which the inhibitor bridges the two active site nickel ions. The inhibition results obtained for K. aerogenes urease are compared with inhibition studies of other ureases and are interpreted in terms of a model for catalysis proposed for the jack bean enzyme (Dixon, N.E., Riddles, P.W., Gazzola, C., Blakely, R.L., and Zerner, B. (1980) Can. J. Biochem. 58, 1335-1344).
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PMID:Competitive inhibitors of Klebsiella aerogenes urease. Mechanisms of interaction with the nickel active site. 267 18