Interaction of Nucleotides with Liver Uridine Diphosphate-glucose-4′-epimerase

Abstract

Abstract UDP-d-glucose-4'-epimerase from calf liver has been obtained in highly purified form by conventional procedures and affinity chromatography using 3-picolylamine analogue of DPN linked to Sepharose. The enzyme has a molecular weight of 70,000 and is a dimer. The enzyme binds all DPN analogues which contain the ADP-ribose portion of DPN. Enzyme containing bound DPNH and to a lesser extent ADP-ribose, or 3-pyridine aldehyde-DPN forms very tight ternary complexes with UDP-galactose, but enzyme containing 3-acetylpyridine-DPN or thionicotinamide-DPN does not bind substrate tightly. In a normal catalytic cycle, DPN only dissociates once in every 9,000 catalytic events. Evidence has been obtained suggesting multiple conformation of the enzyme, induced by different coenzyme analogues, but only DPN induces a conformation which results in enzyme activity.