Mechanism of enzymatic oxidation of purines.

Tautomeric forms of 2-hydroxypurine, in which the structure has been fixed by introduction of an N-methyl group, are oxidized differently by xanthine oxidase. The 1-methyl derivative is attacked at position 8 and the 3-methyl derivative at carbon atom 6. These observations indicate that 2-hydroxypurine itself reacts in a tautomeric form, corresponding to the structure of its 1-methyl derivative.