Fructose 2,6-bisphosphate biosynthesis and regulation of carbohydrate metabolism inAspergillus oryzae

Abstract

The biosynthesis and role of fructose 2,6-bisphosphate (Fru-2,6-P2) in carbohydrate metabolism during induction of an amylolytic system in Aspergillus oryzae was studied. Fluctuations in Fru-2,6-P2were not dependent on the external glucose concentration during induction, whereas the level of Fru-2,6-P2increased significantly when the oxygen concentration was diminished. Phosphofructokinase II (PFK II) of A. oryzae was sensitive to phosphorylation in vitro by the catalytic subunit of cyclic AMP dependent protein kinase, which increased the Vmax(twofold), although the Km(0.7 mM) remained unchanged. Phosphofructokinase I was neither activated by micromolar Fru-2,6-P2nor inhibited by high ATP concentrations. The activity of fructose-1,6-bisphosphatase (FBPase) was subject to strong inhibition by Fru-2,6-P2. Addition of glucose to cultures under gluconeogenic conditions caused a decrease of approximately 40% in the FBPase activity within 4 min. These results indicate that the effect of Fru-2,6-P2in A. oryzae could preferentially control gluconeogenesis. The addition of 0.1 M glucose under gluconeogenic culture conditions also showed that Fru-2,6-P2fluctuations appeared to be, at least in short term, more closely related to temporal changes in the hexose-6-phosphate concentration.Key words: Aspergillus oryzae; fructose-2,6-bisphosphate; phosphofructokinase II (PFK II); cyclic AMP; gluconeogenesis control.