SOME CHARACTERISTICS AND DEVELOPMENTAL ASPECTS OF RAT URIDINE DIPHOSPHOGALACTOSE 4-EPIMERASE

UDP-Gal 4-epimerase (EC 5.1.3.2) activity in developing rat liver, gut, kidney and brain was studied. The assay involved the thin-layer chromatographic separation of sugar nucleotides on polyethyleneimine-impregnated cellulose. UDP-[14C]Gal, the substrate, was converted to UDP-[14C]Glc by the epimerase reaction. Since both the reactant and the product have the same RF value, the UDP-Glc is converted by UDP-Glc dehydrogenase to UDP-GlCUA which is easily distiguished from the UDP-Gal on these plates. Differential centrifugation localized epimerase activity from newborn and adult rat liver in the soluble fraction. Newborn liver had greater specific activity than any other tissue examined, while adult gut had the highest activity of any adult tissue. The activity of the newborn liver declined at Day 2, remaining at the same level until Day 16 when a precipitous decline to adult levels of activity by Day 20 occured. Brain and kidney had lower specific activity than found in liver. No differences in activity of liver enzyme were noted between male and female newborn or adults. The newborn enzyme had a υmax five times greater than the adult, but both enzyme preparations had the same (a) stability characteristics, (b) Km values for UDP-Gal (0.153 mM) and for UDP-Glc (0.5 mM), (c) pH optimum (8.3-8.65) and (d) requirement for exogenous NAD+. Further, both were inhibited by NADH, p-chloromercuribenzoate, UDP-Man, UMP and TDP-Glc, and both exhibited product inhibition with UDP-Glc. © 1969.