Substrate Specificity at the Molybdenum Site in 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. In addition to the binding pocket amino acids, there are several factors that affect the progression of substrates. Therefore, the study is mainly focused to identify the factors affecting the binding stage of catalysis. The activity of xanthine oxidase family enzymes greatly depends on the proper orientation of the substrates and their interaction sites. Therefore, the rate of formation of substrate- enzyme complex is proposed to be affected by the proper orientation and the interaction site of the substrate. Moreover, the keto and enol forms of substrates as well as the existence of the substituent groups affect the reactivity of xanthine oxidase. Thus, the rate of the reaction is proposed to be affected by these factors. The variable activities of the substrates towards xanthine oxidase enzyme are largely due to the factors that affect the reductive half-reaction such as proper orientation of substrates, binding sites, activation of the active site, toutomeric nature of substrates and the inductive and steric effects. This work is used to provide valuable information that may have a mechanistic importance in establishing the substrate preferences of bmXOR to RcXDH and AOR type of enzymes in order to relate electronic structure contributions to enzymatic catalysis.