Uridine Diphosphate Glucose Synthase from Calf Liver. Determinants of Enzyme Activity in Vitro

Peter J. Roach, Kenneth R. Warren, Daniel E. Atkinson

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12 Scopus citations

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 UDP-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 A·TP, ADP, and AMP, had no effect. Over a range of concentrations of UTP (0.04-0.8 mM) and UDP-glucose (0.05-0.3 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.

Original languageEnglish (US)
Pages (from-to)5445-5450
Number of pages6
JournalBiochemistry
Volume14
Issue number25
DOIs
StatePublished - Dec 1 1975
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry

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