This paper is only available as a PDF. To read, Please Download here.
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.
REFERENCES
- Nucleotide Metabolism. Academic Press, New York1973
- Biochem. Pharmacol. 1966; 15: 863
- The Pharmacological Basis of Therapeutics. 5th ed. McMillan Publishing Co., New York1975: 352-355
- J. Biol. Chem. 1948; 172: 349-350
- J. Biol. Chem. 1949; 180: 399-410
- J. Biol. Chem. 1948; 174: 771-772
- J. Biol. Chem. 1970; 245: 2837-2844
- Biochem. J. 1981; 195: 753-760
- Biochem. J. 1978; 171: 653-658
- Biochemistry. 1976; 15: 4451-4457
- J. Biol. Chem. 1955; 216: 405-412
- J. Biol. Chem. 1949; 181: 255-271
- J. Biol. Chem. 1968; 243: 5368-5373
- J. Biol. Chem. 1979; 254: 9927-9932
- Arch. Biochem. Biophys. 1978; 190: 662-670
- Cancer Res. 1969; 29: 737-747
- Mol. Pharmacol. 1969; 5: 318-332
Article Info
Publication History
Published online: January 10, 1984
Identification
Copyright
© 1984 ASBMB. Currently published by Elsevier Inc; originally published by American Society for Biochemistry and Molecular Biology.
User License
Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0) | How you can reuse
Elsevier's open access license policy
Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0)
Permitted
For non-commercial purposes:
- Read, print & download
- Redistribute or republish the final article
- Text & data mine
- Translate the article (private use only, not for distribution)
- Reuse portions or extracts from the article in other works
Not Permitted
- Sell or re-use for commercial purposes
- Distribute translations or adaptations of the article
Elsevier's open access license policy





