Nucleoside Diphosphate-sugar 4-Epimerases I. Uridine Diphosphate Glucose 4-Epimerase of Wheat Germ |
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| Authors: | Fan D F Feingold D S |
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| Affiliation: | Department of Microbiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213. |
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| Abstract: | Uridine diphosphate (UDP)-glucose 4-epimerase (EC 5.1.3.2) has been purified over 1000-fold from extracts of wheat germ by MnCl2 treatment, (NH4)2SO4 fractionation, Sephadex column chromatography, and adsorption onto and elution from calcium phosphate gel. The enzyme has a pH optimum of 9.0. Km values are 0.1 mm for UDP-d-galactose and 0.2 mm for UDP-d-glucose. NAD is required for activity; Ka = 0.04 mm. NADH is an inhibitor strictly competitive with NAD; Ki = 2 μm. Wheat germ also contains UDP-l-arabinose 4-epimerase (EC 5.1.3.5) and thymidine diphosphate (TDP)-glucose 4-epimerase which are distinct from UDP-glucose 4-epimerase. |
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