title: A new method of assessing rates of the futile cycle during glycolytic and gluconeogenic metabolism.
abstract: A method for assessing rates of the futile cycle is presented, and it is illustrated in vitro. Glycolytic- and gluconeogenic-type futile cycles are simulated for the reactions catalyzed by phosphofructokinase (EC 2.7.1.11) and fructose-1,6-bisphosphatase (EC 3.1.3.11) in assays systems in which the cycle rates in either direction can be varied and determined. While either system is sustaining a net flux of carbons in a given direction, the flux of radioactively labeled carbons in the opposite direction is determined. Different cycle rates are obtained by varying phosphofructokinase activity while keeping fructose-1,6-bisphosphatase activity constant in the "gluconeogenic" simulation and varying fructose-1,6-bisphosphatase while keeping phosphofructokinase activity constant in the "glycolytic" simulation. A direct, linear relationship was found between the cycle rate and the radioactive labeling of fructose 1,6-bisphosphate from [U-14C]glucose 6-phosphate during net gluconeogenic carbon flux. Also, a direct, linear relationship was found between cycle rate and radioactive labeling of fructose-6-P from [U-14C]fructose-1,6-bisP during net glycolytic carbon flux. The applicability, advantages, and problems of the method are discussed.
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago.
authors.forename: J C
authors.initials: JC
authors.lastname: Torres
authors.forename: V
authors.initials: V
authors.lastname: Guixé
authors.forename: J
authors.initials: J
authors.lastname: Babul
mesh_terms: D000818:Animals; D006597:Fructose-Bisphosphatase / Q000378:metabolism*; D005943:Gluconeogenesis; D006019:Glycolysis; D006706:Homeostasis; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007934:Leuconostoc / Q000201:enzymology; D008433:Mathematics; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000201:enzymology; D010732:Phosphofructokinase-1 / Q000378:metabolism*; D011770:Pyruvate Kinase / Q000378:metabolism; D011817:Rabbits
chemical_list: D007770:L-Lactate Dehydrogenase; D010732:Phosphofructokinase-1; D011770:Pyruvate Kinase; D006597:Fructose-Bisphosphatase