The conversion of glucose into glucose 6-phosphate in an extract of isolated rat hepatocytes incubated in the presence of MgATP was studied spectrophotometrically at 340nm and also by a radiochemical procedure based on the release of 3H from [2-3H]glucose. Both methods gave similar results. The glucose-saturation curve was sigmoidal and the shape of this curve was not influenced by the ionic composition of the incubation medium. The activity at 0.5mm-glucose was only 1–2% of Vmax., indicating a virtual absence of low-Km hexokinase in the preparation. The radiochemical method was also used for the determination of glucose phosphorylation by intact hepatocytes. The glucose-saturation curve was also markedly sigmoidal, but the s0.5 (substrate concentration at half-maximal velocity) and the Hill coefficient were larger than in extracts of hepatocytes. These two parameters became smaller when cells were incubated in a medium in which Na+ ions were replaced by K+ ions. The increased rate of phosphorylation at low glucose concentration in a K+ medium was accompanied by an increased rate of metabolite recycling between glucose and glucose 6-phosphate and also by an increased uptake of glucose. In both media phosphorylation of glucose was inhibited co-operatively by N-acetylglucosamine. Calculations indicate that this inhibition would reach 100% at saturation of the inhibitor, although at lower concentrations of N-acetylglucosamine it was smaller than expected from the known Ki of N-acetylglucosamine for glucokinase. The rate of phosphorylation of glucose was proportional to the amount of glucokinase in hepatocytes from newborn rats and in conditions such as starvation and diabetes in which the total amount of glucokinase in the liver is decreased. In the same conditions, glucose 6-phosphatase activity was either normal or increased. It is concluded that the phosphorylation of glucose in isolated hepatocytes follows sigmoidal kinetics, which can be explained by the activity of glucokinase alone with no participation of low-Km hexokinase or of glucose 6-phosphatase.
Skip Nav Destination
Article navigation
August 1978
-
Cover Image
Cover Image
- PDF Icon PDF LinkFront Matter
- PDF Icon PDF LinkTable of Contents
- PDF Icon PDF LinkAdvertising
Research Article|
August 15 1978
Phosphorylation of glucose in isolated rat hepatocytes. Sigmoidal kinetics explained by the activity of glucokinase alone
Françoise Bontemps;
Françoise Bontemps
1Laboratoire de Chimie Physiologique, Université de Louvain and International Institute of Cellular and Molecular Pathology, U.C.L., 75.39., Avenue Hippocrate 75, B-1200 Brussels, Belgium
Search for other works by this author on:
Louis Hue;
Louis Hue
1Laboratoire de Chimie Physiologique, Université de Louvain and International Institute of Cellular and Molecular Pathology, U.C.L., 75.39., Avenue Hippocrate 75, B-1200 Brussels, Belgium
Search for other works by this author on:
Henri-Géry Hers
Henri-Géry Hers
1Laboratoire de Chimie Physiologique, Université de Louvain and International Institute of Cellular and Molecular Pathology, U.C.L., 75.39., Avenue Hippocrate 75, B-1200 Brussels, Belgium
Search for other works by this author on:
Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1978 London: The Biochemical Society
1978
Biochem J (1978) 174 (2): 603–611.
Citation
Françoise Bontemps, Louis Hue, Henri-Géry Hers; Phosphorylation of glucose in isolated rat hepatocytes. Sigmoidal kinetics explained by the activity of glucokinase alone. Biochem J 15 August 1978; 174 (2): 603–611. doi: https://doi.org/10.1042/bj1740603
Download citation file:
Sign in
Don't already have an account? Register
Sign in to your personal account
You could not be signed in. Please check your email address / username and password and try again.
Captcha Validation Error. Please try again.