Fructose 1-phosphate and the regulation of glucokinase activity in isolated hepatocytes.
Fructose 1-phosphate kinase was partially purified from Clostridium difficile and used to develop specific assays of fructose 1-phosphate and fructose. The concentration of fructose 1-phosphate was below the detection limit of the assay (25 pmol/mg protein) in hepatocytes incubated in the presence of glucose as sole carbohydrate. Addition of fructose (0.05-1 mM) caused a concentration-dependent and transient increase in the fructose 1-phosphate content. Glucagon (1 microM) and ethanol (10 mM) caused a severalfold decrease in the concentration of fructose 1-phosphate in cells incubated with fructose, whereas the addition of 0.1 microM vasopressin or 10 mM glycerone, or raising the concentration of glucose from 5 mM to 20 mM had the opposite effect. All these agents caused changes in the concentration of triose phosphates that almost paralleled those of the fructose 1-phosphate concentration. Sorbitol had a similar effect to fructose in causing the formation of fructose 1-phosphate. D-Glyceraldehyde was much less potent in this respect than the ketose and its effect disappeared earlier. The effect of D-glyceraldehyde was reinforced by an increase in the glucose concentration and decreased by glucagon. Both fructose and D-glyceraldehyde stimulated the phosphorylation of glucose as estimated by the release of 3H2O from [2-3H]glucose, but the triose was less potent in this respect than fructose and its effect disappeared earlier. Glucagon and ethanol antagonised the effect of low concentrations of fructose or D-glyceraldehyde on the detritiation of glucose. These results support the proposal that fructose 1-phosphate mediates the effects of fructose, D-glyceraldehyde and sorbitol by relieving the inhibition exerted on glucokinase by a regulatory protein.
Davies
D R
DR
Laboratoire de Chimie physiologique, International Institute of Cellular and Molecular Pathology, Brussels, Belgium.
Detheux
M
M
Van Schaftingen
E
E
D000818:Animals; D002478:Cells, Cultured; D003013:Clostridium / Q000201:enzymology; D000431:Ethanol / Q000494:pharmacology; D005636:Fructosephosphates / Q000032:analysis / Q000378:metabolism*; D005934:Glucagon / Q000494:pharmacology; D005941:Glucokinase / Q000378:metabolism*; D006706:Homeostasis; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D010732:Phosphofructokinase-1 / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats
D005636:Fructosephosphates; C032284:fructose-1-phosphate; D000431:Ethanol; D005934:Glucagon; D010732:Phosphofructokinase-1; D005941:Glucokinase