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 radioautoradiography after separation of the sugar nucleotides by paper chromatography ot t.l.c. The pH optimum and the Km values for UDP-glucose 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.
Biosynthesis of glycosaminoglycans: uridine diphosphate glucose 4'-epimerase from cornea and epiphysial-plate cartilage
SPEZIALE, PIETRO;BALDUINI, CESARE;
1975-01-01
Abstract
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 radioautoradiography after separation of the sugar nucleotides by paper chromatography ot t.l.c. The pH optimum and the Km values for UDP-glucose 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
