Biosynthesis of glycosaminoglycans: uridine diphosphate glucose 4'-epimerase from cornea and epiphysial-plate cartilage.
UDP-glucose 4'-epimerase (EC 5.1.3.2.) was extracted from newborn-pig epiphysial-plate cartilage and whole bovine cornea. The formation of radioactive UDP-galactose from UDP[U-14C]glucose was demonstrated by radioautography after separation of the sugar nucleotides by paper chromatography or t.l.c. The pH optimum and the Km values for UDP-glucose, UDP-galactose and NAD+ were determined in both tissues. UDP-galactose and UDP-glucuronic acid formation after incubation with different UDP-glucose concentrations was followed; the same experiment was carried out using different UDP-galactose concentrations and following the formation of UDP-glucose and UDP-glucuronic acid. At equilibrium, the ratio UDP-glucose/UDP-galactose reaches a value of about 3.5. The results obtained seem to indicate that UDP-glucose 4'-epimerase activity is strongly dependent on that of UDP-glucose dehydrogenase. The physiological meaning of UDP-glucose 4'-epimerase in glycosaminoglycan biosynthesis in the two tissues under study is discussed on the basis of the Km values of UDP-glucose 4'-epimerase and UDP-glucose dehydrogenase and on the basis of the rate of UDP-glucose and UDP-galactose utilization.
D000818:Animals; D002238:Carbohydrate Epimerases / Q000378:metabolism*; D002356:Cartilage / Q000201:enzymology*; D002417:Cattle; D002809:Chondroitin Sulfates / Q000378:metabolism; D003315:Cornea / Q000201:enzymology*; D006025:Glycosaminoglycans / Q000096:biosynthesis*; D007632:Keratan Sulfate / Q000378:metabolism; D013552:Swine; D014534:UDPglucose 4-Epimerase / Q000378:metabolism*
D006025:Glycosaminoglycans; D002809:Chondroitin Sulfates; D007632:Keratan Sulfate; D002238:Carbohydrate Epimerases; D014534:UDPglucose 4-Epimerase