J. Biol. Chem., Vol. 259, Issue 1, 12-15, Jan, 1984

Inhibition of mammalian xanthine oxidase by folate compounds and amethopterin

AS Lewis, L Murphy, C McCalla, M Fleary and S Purcell

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.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				G. Zaza, M. Cheok, W. Yang, J. C. Panetta, C.-H. Pui, M. V. Relling, and W. E. Evans Gene expression and thioguanine nucleotide disposition in acute lymphoblastic leukemia after in vivo mercaptopurine treatment Blood, September 1, 2005; 106(5): 1778 - 1785. [Abstract] [Full Text] [PDF]

				M. Benchalal, E. Yahchouchy-Chouillard, S. Fouere, and A. Fingerhut Anaphylactic shock secondary to intravenous administration of folinic acid: a first report Ann. Onc., March 1, 2002; 13(3): 480 - 481. [Abstract] [Full Text] [PDF]

				K. Kawashima, K. Hosoi, T. Naruke, T. Shiba, M. Kitamura, and T. Watabe Aldehyde Oxidase-Dependent Marked Species Difference in Hepatic Metabolism of the Sedative-Hypnotic, Zaleplon, Between Monkeys and Rats Drug Metab. Dispos., March 1, 1999; 27(3): 422 - 428. [Abstract] [Full Text]