%0 Journal Article %J Journal of computer-aided molecular design %D 1997 %T Role of tautomerism of 2-azaadenine and 2-azahypoxanthine in substrate recognition by xanthine oxidase %A Hernandez,B. %A M. Orozco %A F. J. Luque %K Adenine/analogs & derivatives/chemistry; Binding Sites; Gases; Hypoxanthines/chemistry; Isomerism; Models %K Molecular; Molecular Structure; Solutions; Substrate Specificity; Thermodynamics; Water; Xanthine Oxidase/chemistry/metabolism %N 2 %P 153 - 162 %V 11 %X The tautomerism of 2-azaadenine and 2-hypoxanthine has been examined in the gas phase and in aqueous solution. The tautomerism in the gas phase has been studied by means of semiempirical and ab initio quantum-mechanical computations, as well as density-functional calculations. The influence of the aqueous solvent on the relative stability between tautomers has been estimated from self-consistent reaction field calculations performed with different high-level continuum models. The results provide a detailed picture of the tautomeric preference for these purine bases. The importance of tautomerism in the substrate recognition by xanthine oxidase is discussed. Finally, the rate of oxidation of 2-azaadenine and 2-hypoxanthine by xanthine oxidase is discussed in terms of the recognition model at the enzyme active site. %8 1997/03//