title: Regulatory role of fructose-2,6-bisP on glucose metabolism in frog oocytes: in vivo inhibition of glycogen synthesis.
abstract: Glycogen synthesis following glucose microinjection in frog oocytes proceeds preferentially by an indirect pathway involving gluconeogenesis from triose compounds. Because of the known regulatory role of fructose-2,6-bisP on glucose utilization in most vertebrate tissues we coinjected [U-14C]glucose and fructose-2,6-bisP into oocytes and observed a marked inhibition of label incorporation into glycogen, with an I50 value of 2 microM, which is similar to the value measured for the in vitro inhibition of oocyte fructose-1,6-bisphosphatase. Other hexoses-bisP were tested: 2,5-anhydromannitol-1,6-bisP was as effective as inhibitor as fructose-2,6-bisP; glucose-1,6-bisP showed some effect although 50% inhibition was obtained at a concentration 10 times higher than with fructose-2,6-bisP; fructose-1,6-bisP had no effect at all. The inhibition pattern for the in vivo glycogen synthesis by these analogs closely matched the one obtained with partially purified oocyte fructose-1,6-bisphosphatase. The intracellular concentration of fructose-2,6-bisP in unperturbed oocytes was found to be between 0.1 and 0.2 microM. Fructose-6-phosphate,2-kinase levels measured in oocyte homogenates were between 0.02 and 0.06 mU per gram of ovary. After 60 min incubation, fructose-2,6-bisP microinjected into the oocytes was almost completely degraded, suggesting that fructose-2,6-bisphosphatase is active in vivo. The results presented in this paper indicate that fructose-2,6-bisP plays an important role in the in vivo regulation of glucose utilization in frog-grown oocytes.
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: V
authors.initials: V
authors.lastname: Guixé
authors.forename: A
authors.initials: A
authors.lastname: Preller
authors.forename: E
authors.initials: E
authors.lastname: Kessi
authors.forename: T
authors.initials: T
authors.lastname: Ureta
mesh_terms: D000818:Animals; D001001:Anura; D002250:Carbon Radioisotopes; D005260:Female; D005635:Fructosediphosphates / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism*; D006003:Glycogen / Q000096:biosynthesis*; D007700:Kinetics; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D025481:Phosphofructokinase-2; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D013403:Sugar Phosphates / Q000494:pharmacology
chemical_list: D002250:Carbon Radioisotopes; D005635:Fructosediphosphates; D013403:Sugar Phosphates; C027652:fructose 2,6-diphosphate; D006003:Glycogen; D025481:Phosphofructokinase-2; D010744:Phosphoric Monoester Hydrolases; D005947:Glucose