The Role of Binding Pocket Amino Acid Residues in Substrate Specificity Towards Xanthine Oxidase Enzyme

Xanthine oxidase is one of the most useful molybdenum containing enzymes, which catalyzes a wide range of purine derivative heterocyclic substrates. In order for the interaction between the reactants to take place, the substrates are expected to enter the binding pocket and attain a proper orientation with the help of binding pocket amino acid residues. Therefore, the study is mainly focused to understand the role of binding pocket amino acid residues in providing the substrates proper orientation for the nucleophilic reaction to take place. The binding pocket amino acids residues in particular, Glu 802 and Arg 880 were proposed to create a hydrogen bonding microenvironment and modulate the near attack conformation (NAC) in the presence of substrates. In order to probe the behavior of the substrates, inside the binding pocket, the electronic structure calculations were performed. Moreover, the activation of the active site was proposed to take place after the acidic proton is abstracted from the HOeq by [bmXOR]-Glu 1261. The Oxyanion of the active site is responsible for the nucleophilic attack on the deficient carbon center of the given substrates. In general, the purpose of the study is to relate the roles of amino acid residues in the reactivities of enzyme catalyzed reactions and to determine the most favorable path way during the activation of the active site by Glu 1261