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Modeling the transition state structures of the xanthine oxidase enzyme active site bound to the thioformate

Jenbrie Molla Kessete


Xanthine oxidase enzymes catalyze oxidative reactions in variety of biochemical reactions. This work is focused on predicting the transition state structure of the xanthine oxidase enzyme active site bound to the thioformate. The events at the transition state were probed using DFT method with b3lyp level of theory and also LANL2DZ and 6-31G (d', p’) basis sets were used for molybdenum and none metal atoms respectively. To understand the events taking place at transition state, charge and bond distance parameters were computed. The transition state of none protonated, single protonated and double protonated thioformate bound to the active site, respectively, were confirmed at -1034.3 S-1, -357.56 S-1 and -99.53 S-1 by the one imaginary frequency. The activation for none protonated thioformate bound to the active site is high due to the absence of factors that stabilize the accumulation of charge on substrate at the transition state. The nature of substrate highly affects activation energy of xanthine oxidase enzyme. The study of formate oxidation has mechanistic significance.

Key words: thioformate, modeling, transition state, xanthine oxidase.

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