title: Uridine diphosphate glucose synthase from calf liver: determinants of enzyme activity in vitro.
abstract: The reaction catalyzed by calf liver uridine diphosphate glucose synthase (pyrophosphorylase) (EC 2.7.7.9; UTP + glucose 1-phosphate = UDP-glucose + PPi) is an example of an enzymic reaction in which a nucleoside triphosphate other than ATP is the immediate source of metabolic energy. Kinetic properties of the enzyme, acting in the direction of UCP-glucose formation were investigated in vitro. The reaction was inhibited by UDP-glucose (0.072), Pi (11), UDP (1.6), UDP-xylose (0.87), UDP-glucuronate (1.3), and UDP-galacturonate (0.95). The numbers in parentheses indicate the concentration (mM) required for half-maximal inhibition under the conditions used. Other compounds tested, including ATP, ADP, and AMP, had no effect. Over a range of concentrations of UTP (0.04-0.8 MM) and UDP-glucose (0.05-0.03 mM), the reaction rate was more dependent on the concentration ratio [UDP-glucose]/[UTP] than on the absolute concentration of either compound. Comparison of the kinetic properties in vitro with estimates of metabolite levels in vivo suggests that (1) the enzyme operates in a range far from its maximal rate, and (2) the concentrations of glucose 1-phosphate and Pi and the ratio [UDP-glucose]/[UTP] may be the most important determinants of UDP-glucose synthase activity.
mesh_terms: D000227:Adenine Nucleotides / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D011756:Diphosphates / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005958:Glucosephosphates / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009713:Nucleotidyltransferases / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase / Q000378:metabolism*; D014532:Uridine Diphosphate Glucose / Q000494:pharmacology; D014539:Uridine Diphosphate Sugars / Q000494:pharmacology
chemical_list: D000227:Adenine Nucleotides; D011756:Diphosphates; D005958:Glucosephosphates; D010710:Phosphates; D014539:Uridine Diphosphate Sugars; D009713:Nucleotidyltransferases; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase; D014532:Uridine Diphosphate Glucose