Bergmann F, Levene L. Enzymic oxidation of 3-hydroxyxanthine to 3-hydroxyuric acid.
BIOCHIMICA ET BIOPHYSICA ACTA 1977;
481:359-63. [PMID:
15604 DOI:
10.1016/0005-2744(77)90269-8]
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Abstract
1. Bovine milk xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) oxidises 3-hydroxyxanthine slowly to 3-hydroxyuric acid; the 1-methyl derivative of 3-hydroxyxanthine is attacked about twice as fast. 2. The pH optimum for the reaction of 2-hydroxyxanthine is near 5, i.e. the neutral form of this substrate is attacked much faster than the anion. Probably in the "active" form of the latter, the negative charge is located mainly in the imidazole ring, thus inhibiting nucleophilic attack at C-8.
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