title: Investigation on the mechanism by which fructose, hexitols and other compounds regulate the translocation of glucokinase in rat hepatocytes.
abstract: In isolated hepatocytes in suspension, the effect of sorbitol but not that of fructose to increase the concentration of fructose 1-phosphate and to stimulate glucokinase was abolished by 2-hydroxymethyl-4-(4-N,N-dimethylamino-1-piperazino)-pyrimidine (SDI 158), an inhibitor of sorbitol dehydrogenase. In hepatocytes in primary culture, fructose was metabolized at approximately one-quarter of the rate of sorbitol, and was therefore much less potent than the polyol in increasing the concentration of fructose 1-phosphate and the translocation of glucokinase. In cultures, sorbitol, commercial mannitol, fructose, D-glyceraldehyde or high concentrations of glucose caused fructose 1-phosphate formation and glucokinase translocation in parallel. Commercial mannitol was contaminated by approx. 1% sorbitol, which accounted for its effects. The effects of sorbitol, fructose and elevated concentrations of glucose were partly inhibited by ethanol, glycerol and glucosamine. Mannoheptulose increased translocation without affecting fructose 1-phosphate concentration. Kinetic studies performed with recombinant human beta-cell glucokinase indicated that this sugar, in contrast with N-acetylglucosamine, binds to glucokinase competitively with the regulatory protein. All these observations indicate that translocation is promoted by agents that favour the dissociation of the glucokinase-regulatory-protein complex either by binding to the regulatory protein (fructose I-phosphate) or to glucokinase (glucose, mannoheptulose). They support the hypothesis that the regulatory protein of glucokinase acts as an anchor for this enzyme that slows down its release from digitonin-permeabilized cells.
authors.affiliation: Laboratoire de Chimie Physiologique, Université Catholique de Louvain, Brussels, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Niculescu
authors.forename: M
authors.initials: M
authors.lastname: Veiga-da-Cunha
authors.forename: E
authors.initials: E
authors.lastname: Van Schaftingen
mesh_terms: D000117:Acetylglucosamine / Q000378:metabolism; D000818:Animals; D004098:Dihydroxyacetone / Q000494:pharmacology; D000431:Ethanol / Q000494:pharmacology; D005632:Fructose / Q000494:pharmacology*; D005636:Fructosephosphates / Q000378:metabolism; D005941:Glucokinase / Q000378:metabolism*; D005985:Glyceraldehyde / Q000494:pharmacology; D006601:Hexoses / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D007064:L-Iditol 2-Dehydrogenase / Q000037:antagonists & inhibitors*; D008099:Liver / Q000201:enzymology*; D008297:Male; D008353:Mannitol / Q000378:metabolism; D008356:Mannoheptulose / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D005636:Fructosephosphates; D006601:Hexoses; D011743:Pyrimidines; C103900:SDI 158; C032284:fructose-1-phosphate; D005632:Fructose; D005985:Glyceraldehyde; D000431:Ethanol; D008353:Mannitol; D008356:Mannoheptulose; D007064:L-Iditol 2-Dehydrogenase; D005941:Glucokinase; D004098:Dihydroxyacetone; C030192:tagatose; D000117:Acetylglucosamine