title: UDPGlucose 4-epimerase from Saccharomyces fragilis. Allosteric kinetics with UDP-glucose as substrate.
abstract: UDPglucose 4-epimerase from Saccharomyces fragilis catalyzes a freely reversible reaction between UDP-galactose and UDP-glucose. With UDP-galactose as the substrate the enzyme shows a classical hyperbolic kinetics but when UDP-glucose is used as the substrate a distinct allostericity is observed. As a consequence, at low concentrations of UDP-glucose, the enzyme fails to establish the equilibrium at a significant rate. Glucose 6-phosphate acts as a strong activator for the enzyme with low concentrations of UDP-glucose as the substrate. In view of these rather unusual kinetic data for an enzyme catalyzing a freely reversible reaction, UDPglucose 4-epimerase may play a regulatory role in controlling the flux of galactose metabolism.
mesh_terms: D000494:Allosteric Regulation; D002238:Carbohydrate Epimerases / Q000378:metabolism*; D007700:Kinetics; D012440:Saccharomyces / Q000201:enzymology*; D013997:Time Factors; D014534:UDPglucose 4-Epimerase / Q000378:metabolism*; D014531:Uridine Diphosphate Galactose / Q000494:pharmacology; D014532:Uridine Diphosphate Glucose / Q000494:pharmacology
chemical_list: D014531:Uridine Diphosphate Galactose; D002238:Carbohydrate Epimerases; D014534:UDPglucose 4-Epimerase; D014532:Uridine Diphosphate Glucose