A MECHANISM OF REGULATION OF HEPATIC FRU 2,6-P-2 CONCENTRATION UPON REFEEDING - INVOLVEMENT OF XYLULOSE 5-P AND CYCLIC-AMP

In order to determine the mechanism for delayed increase in Fructose 2 ,6-P-2 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-P-2 and Xylulose 5-P were similar but different from hexose 6-P or glyco,gen in the livers of 48 h star ved rats refed with NIH diet. The increase in the Fructose 2,6-P-2 lev el was a result of a combination of changes in Fructose 6-P,2-kinase a nd Fructose 2,6-bisphosphatase activity ratios, indicating dephosphory lation of the bifunctional enzyme and decreased cAMP. A similar correl ation between Fructose 2,6-P-2 and Xylulose 5-P and dephosphorylation was observed with refeeding high sucrose diet and also with 16 h starv ed rats. These kinetic results are consistent with the idea that a spe cific protein phosphatase 2A, activated by Xylulose 5-P, dephosphoryla tes Fructose 6-P,2-kinase:Fructose 2,6-bisphosphatase and also decreas ed protein kinase A activity, resulting in increased hepatic Fructose 2,6-P-2. (C) 1996 Academic Press, Inc.