Regulation of glucokinase by a fructose-1-phosphate-sensitive protein in pancreatic islets.
In the post-microsomal supernatant of pancreatic islets, prepared from fasted or fed rats, D-fructose 1-phosphate increased the activity of glucokinase by 20-30% as measured in the presence of D-glucose 6-phosphate and D-fructose 6-phosphate. Such an activation was less marked than that found in liver extracts. The islet cytosol was also found to inhibit purified liver glucokinase, and this effect was antagonized by D-fructose 1-phosphate. In the presence of hexose 6-phosphates, partially purified islet glucokinase was inhibited by the hepatic glucokinase regulatory protein in a D-fructose-1-phosphate-sensitive manner. In intact islets, D-glyceraldehyde stimulated the generation of 14C-labelled D-fructose 1-phosphate from D-[U-14C]glucose and increased the production of 3H2O from D-[5-3H]glucose. These findings suggest that the activity of glucokinase in islet cells may be regulated by a protein mediating the antagonistic effects of D-fructose 6-phosphate and D-fructose 1-phosphate in a manner qualitatively similar to that operating in hepatocytes, but with lower efficiency.
Malaisse
W J
WJ
Laboratory of Experimental Medicine, Brussels Free University, Belgium.
Malaisse-Lagae
F
F
Davies
D R
DR
Vandercammen
A
A
Van Schaftingen
E
E
D000818:Animals; D003600:Cytosol / Q000201:enzymology; D004435:Eating; D005215:Fasting; D005636:Fructosephosphates / Q000494:pharmacology*; D005941:Glucokinase / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism; D006600:Hexosephosphates / Q000494:pharmacology; D006706:Homeostasis; D007515:Islets of Langerhans / Q000201:enzymology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009928:Organ Specificity; D011506:Proteins / Q000502:physiology*; D051381:Rats
D005636:Fructosephosphates; D006600:Hexosephosphates; D011506:Proteins; C032284:fructose-1-phosphate; D006593:Hexokinase; D005941:Glucokinase