The regulation of 6-phosphofructo-1-kinase by insulin and glucagon in isolated hepatocytes of the American eel.
Kinetic characteristics of American eel liver 6-phosphofructo-1-kinase (PFK-1) and the effects of porcine insulin, bovine glucagon, and dibutyryl-cAMP were studied. At 0.1 mM ATP, kinetics were sigmoidal with respect to fructose-6-phosphate (F-6-P) concentrations and the S0.5 (F-6-P) increased with higher ATP concentrations. At 2 mM F-6-P, optimal ATP concentrations were 0.1 mM, with maximal inhibition at 0.5 mM. Fructose 2,6-bisphosphate (Fru-2,6-P2) offset ATP inhibition and activated the enzyme, changing F-6-P kinetic curves from sigmoidal to hyperbolic. At 2 mM F-6-P and 0.1 mM ATP the Fru-2,6-P2 activation curve was hyperbolic with a Ka of approximately 1 microM. In isolated hepatocytes, porcine insulin decreased the sensitivity of PFK-1 to ATP, an effect that was offset when bovine glucagon was also present. Insulin, alone and with glucagon, increased the Fru-2,6-P2 activation ratio. In the presence of glucagon, insulin increased Fru-2,6-P2 concentrations in hepatocytes. These effects suggest that PFK-1 is a potential regulatory point for hormones in the control of carbohydrate metabolism in the American eel liver.
Foster
G D
GD
Department of Biology, University of Ottawa, Ontario, Canada.
Storey
K B
KB
Moon
T W
TW
D000811:Anguilla / Q000378:metabolism*; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D005635:Fructosediphosphates / Q000378:metabolism; D005934:Glucagon / Q000494:pharmacology*; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D010732:Phosphofructokinase-1 / Q000378:metabolism*
D005635:Fructosediphosphates; D007328:Insulin; D003994:Bucladesine; C027652:fructose 2,6-diphosphate; D005934:Glucagon; D010732:Phosphofructokinase-1