REGULATORY ROLE OF FRUCTOSE-2,6-BISP ON GLUCOSE-METABOLISM IN FROG OOCYTES - IN-VIVO INHIBITION OF GLYCOGEN-SYNTHESIS

Glycogen synthesis following glucose microinjection in frog oocytes pr oceeds preferentially by an indirect pathway involving gluconeogenesis from triose compounds. Because of the known regulatory role of fructo se-2,6-bisP on glucose utilization in most vertebrate tissues we coinj ected [U-C-14]glucose and fructose-2,6-bisP into oocytes and observed a marked inhibition of label incorporation into glycogen, with an I-50 value of 2 mu M, which is similar to the value measured for the in vi tro inhibition of oocyte fructose-1,6-bisphosphatase. Other hexoses-bi sP were tested: 2,5-anhydromannitol-1,6-bisP was as effective as inhib itor as fructose-2,6-bisP; glucose-1,6-bisP showed some effect althoug h 50% inhibition was obtained at a concentration 10 times higher than with fructose-2,6-bisP; fructose-l,6-bisP had no effect at all, The in hibition pattern for the in vivo glycogen synthesis by these analogs c losely matched the one obtained with partially purified oocyte fructos e-1,6-bisphosphatase. The intracellular concentration of fructose-2,6- bisP in unperturbed oocytes was found to be between 0.1 and 0.2 mu M. Fructose-6-phosphate,2-kinase levels measured in oocyte homogenates we re 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 complete ly degraded, suggesting that fructose-2,6-bisphosphatase is active in vivo. The results presented in this paper indicate that fructose-2,6-b isP plays an important role in the in vivo regulation of glucose utili zation in frog-grown oocytes. (C) 1997 Academic Press.