Uridine diphosphate glucose dehydrogenase of calf liver. Properties and inhibition characteristics with uridine diphosphate xylose analogues

UDP-glucose dehydrogenase of calf liver dissociated in guanidine-HCl into six subunits. The number of reactive sulfhydrylgroups of native and guanidine-HCl-treated enzyme was found to be 20 ± 1 and 46 ± 1, respectively, per mole of native enzyme. A crude preparation of UDP-glucose pyrophosphorylase from yeast was used for the preparation of 5-hydroxyuridine diphosphate xylose and 5-aminouridine diphosphate xylose. 5,6-Dihydrouridine diphosphate xylose was prepared by catalytic reduction of UDP-xylose. The nature of the inhibition produced by UDP-xylose or its analogues was similar with respect to either UDP-glucose or NAD⁺, the two substrates for the enzyme. Hydrogenation of the 5,6-double bond or substitution of a hydroxyl group at the C-5 position of the pyrimidine portion of UDP-xylose decreased its inhibitory activity. Substitution of an amino group at the C-5 position, however, did not alter the activity of the allosteric inhibitor.