Catalytic mechanism of human UDP-glucose 6-dehydrogenase: in situ proton NMR studies reveal that the C-5 hydrogen of UDP-glucose is not exchanged with bulk water during the enzymatic reaction.

ABSTRACT: Human UDP-glucose 6-dehydrogenase (hUGDH) catalyzes the biosynthetic oxidation of UDP-glucose into UDP-glucuronic acid. The catalytic reaction proceeds in two NAD(+)-dependent steps via covalent thiohemiacetal and thioester enzyme intermediates. Formation of the thiohemiacetal adduct occurs through attack of Cys(276) on C-6 of the UDP-gluco-hexodialdose produced in the first oxidation step. Because previous studies of the related enzyme from bovine liver had suggested loss of the C-5 hydrogen from UDP-gluco-hexodialdose due to keto-enol tautomerism, we examined incorporation of solvent deuterium into product(s) of UDP-glucose oxidation by hUGDH. We used wild-type enzyme and a slow-reacting Glu(161)→Gln mutant that accumulates the thioester adduct at steady state. In situ proton NMR measure

SUBMITTER: Eixelsberger T 

PROVIDER: S-EPMC3387377 | biostudies-literature | 2012 Jul

REPOSITORIES: biostudies-literature