Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In response to a recent report (Lewis, A.S., Murphy, L., Mcalla, C., Fleary, M., and Purcell, S. (1984) J. Biol. Chem. 259, 12-15) that folic acid was a potent inactivator of xanthine oxidase, the details of this apparent inactivation were studied. In confirmation, we also found that commercially available folic acid produced a time-dependent progressive inhibition (apparent inactivation) of xanthine oxidase. A plot of the pseudo-first order rate constant of the decay of enzyme activity versus the concentration of folic acid resulted in a straight line. This indicated that the progressive inhibition was caused by a slow second order combination of an inhibitor with the enzyme. The second order rate constant for this association (slope of replot) was 5.7 X 10(3) M-1 S-1. The slowness of this constant together with the observation that complete inactivation did not occur suggested that the progressive inhibition might be due to the slow binding of a high affinity contaminant. This was corroborated by the finding that the association constant was decreased to 1.6 X 10(2) M-1 S-1 after partially purifying the folic acid. The compound most likely to be producing this inhibition is pterin aldehyde (2-NH2-4-OH-pteridine-6-aldehyde), a photolytic breakdown product of folic acid. Pterin aldehyde was found to be a progressive inhibitor of xanthine oxidase with an association constant of 2.2 X 10(5) M-1 S-1. When the apparent association constants of commercial and purified folic acid were adjusted to reflect the pterin aldehyde content (3.6% and 0.2%, respectively), they became similar to the association constant of pterin aldehyde. Thus, it seems that the apparent inactivation of xanthine oxidase by folic acid was caused by the slow binding of contaminating pterin aldehyde.
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PMID:Folic acid does not inactivate xanthine oxidase. 654 55

We have examined the effects of folate compounds and the folate analog amethopterin (methotrexate) as inhibitors of mammalian xanthine oxidase and have found that they offer potent inhibition of the enzyme. We have compared the inhibitory potency of folic acid and its coenzyme derivative tetrahydrofolic acid to that of allopurinol, a known inhibitor of xanthine oxidase, and have demonstrated that folic acid and tetrahydrofolic acid are severalfold more potent than allopurinol as inhibitors of xanthine oxidase. Comparative inhibition constants calculated were 5.0 X 10(-7) M for folic acid. 1.25 X 10(-6) M for tetrahydrofolic acid, and 4.88 X 10(-6) M for allopurinol. Incubation of xanthine oxidase with folic acid at a concentration of 10(-6) M abolished 94% of the enzymic activity within 1 min of incubation with the enzyme. At the same concentration, allopurinol was almost ineffective as an inhibitor of xanthine oxidase. The substrate xanthine protected the enzyme against total inhibition by folic acid. Reversibility of the enzymic inhibition by folic acid was demonstrated. Folic acid-inactivated enzyme was totally regenerated either by filtration through Sephadex G-200 or by precipitation with ammonium sulfate. 2-Amino-4-hydroxypteridine was a poor substrate for the enzyme but a potent inhibitor for the oxidation of xanthine by the enzyme. The inhibition constant calculated was 1.50 X 10(-6) M. In the presence of an excess of xanthine oxidase, neither folic acid nor tetrahydrofolic acid and allopurinol exhibited any change in intensity of their absorbance or in the wavelength of their maximal absorbance that might have been suggestive of substrate utility. The folate analog amethopterin was also determined a potent inhibitor of mammalian xanthine oxidase. The inhibition constant calculated was 3.0 X 10(-5) M.
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PMID:Inhibition of mammalian xanthine oxidase by folate compounds and amethopterin. 660 20

An enzymatic inhibition assay for the xanthine oxidase (XOD) inhibitors allopurinol and oxipurinol is described. 2-Amino-4-hydroxypteridine is used as sensitive fluorogenic substrate, which is oxidized to highly fluorescent isoxanthopterin by XOD. Increasing concentrations of allopurinol (Ap) or oxipurinol (Ox) prevent conversion of 2-amino-4-hydroxypterdine to isoxanthopterin. Assay conditions of XOD-inhibition are different for Ap and Ox. In the presence of xanthine both Ap and Ox inhibit XOD to the same degree; absence of xanthine results in inactivation by Ap only. Thus rapid and convenient determination of Ap and Ox is possible without prior separation of the substances. The limit of detection is about 0.5 nmol/ml (50 micrograms/ml) in serum and 25 nmol/ml (2.5 micrograms/ml) in urine.
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PMID:Enzymatic inhibition assay for fluorometric determination of allopurinol and oxipurinol in serum and urine. 689 32

The reactivity and toxicity of nitric oxide is modest in comparison to oxidants derived from nitric oxide. Exposure of Escherichia coli to 1 mM nitric oxide under aerobic or anaerobic conditions did not decrease viability of the bacteria. Peroxynitrite (1 mM), the reaction product of superoxide and nitric oxide, was completely bactericidal after 5 s. The nitrovasodilator, 3-morpholinosydnonimine-N-ethylcarbamide (SIN-1), slowly decomposes to release both nitric oxide and superoxide and thereby produces peroxynitrite. SIN-1 killed E. coli in direct proportion to its concentration with an LD50 of 0.5 mM. Copper, zinc superoxide dismutase (50-400 units/ml) provided substantial but not complete protection against SIN-1 killing. Catalase (500-10,000 units/ml) partially protected in direct proportion to its concentration, while inactivated catalase was not protective. Superoxide dismutase and catalase together completely protected E. coli against SIN-1 toxicity. Oxy-hemoglobin eliminated both SIN-1 and peroxynitrite toxicity. The bactericidal activity of SIN-1 was further enhanced by pterin plus xanthine oxidase. Pterin plus xanthine oxidase alone or together with Fe3+ ethylenediamine tetraacetate produced no significant decrease in E. coli viability. Hydrogen peroxide was not directly toxic to the bacteria, but E. coli pretreated with hydrogen peroxide were more susceptible to peroxynitrite, SIN-1, and the aerobic oxidation products of nitric oxide. Hydrogen peroxide pretreatment did not increase significantly the toxicity of nitric oxide under anaerobic conditions. Our results suggest that peroxynitrite is far more toxic to E. coli than nitric oxide or its by products from aerobic oxidation.
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PMID:The comparative toxicity of nitric oxide and peroxynitrite to Escherichia coli. 784 Jun 33