A mechanism of regulation of hepatic Fru 2,6-P2 concentration upon refeeding: involvement of xylulose 5-P and cyclic-AMP.
In order to determine the mechanism for delayed increase in Fructose 2,6-P2 in livers of refed rats, the time course of changes in various metabolites upon refeeding NIH or high sucrose diet was investigated. Kinetics of increase in Fructose 2,6-P2 and Xylulose 5-P were similar but different from hexose 6-P or glycogen in the livers of 48 h starved rats refed with NIH diet. The increase in the Fructose 2,6-P2 level was a result of a combination of changes in Fructose 6-P,2-kinase and Fructose 2,6-bisphosphatase activity ratios, indicating dephosphorylation of the bifunctional enzyme and decreased cAMP. A similar correlation between Fructose 2,6-P2 and Xylulose 5-P and dephosphorylation was observed with refeeding high sucrose diet and also with 16 h starved rats. These kinetic results are consistent with the idea that a specific protein phosphatase 2A, activated by Xylulose 5-P, dephosphorylates Fructose 6-P,2-kinase:Fructose 2,6-bisphosphatase and also decreased protein kinase A activity, resulting in increased hepatic Fructose 2,6-P2.
Liu
Y Q
YQ
Research Service, Department of Veterans Affairs Medical Center, Dallas, Texas USA.
Uyeda
K
K
D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D005502:Food; D005635:Fructosediphosphates / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D010428:Pentosephosphates / Q000378:metabolism*; D025481:Phosphofructokinase-2; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley
D004040:Dietary Carbohydrates; D005635:Fructosediphosphates; D010428:Pentosephosphates; C031625:xylulose-5-phosphate; C027652:fructose 2,6-diphosphate; D000242:Cyclic AMP; D025481:Phosphofructokinase-2; D010744:Phosphoric Monoester Hydrolases