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  • Title: Changes in the concentration of fructose 2,6-bisphosphate in Aspergillus niger during stimulation of acidogenesis by elevated sucrose concentration.
    Author: Kubicek-Pranz EM, Mozelt M, Rohr M, Kubicek CP.
    Journal: Biochim Biophys Acta; 1990 Mar 26; 1033(3):250-5. PubMed ID: 2156568.
    Abstract:
    The presence of fructose 2,6-bisphosphate (Fru-2,6-P2) and phosphofructokinase 2 (PFK 2) were established in the citric-acid-producing filamentous fungus Aspergillus niger. Fru-2,6-P2 levels were around 3.0 (+/- 0.8) nmol per g dry weight during growth on sucrose, and half of this in mycelia grown on citrate as a carbon source. PFK 2 was detected with a specific activity of 150 mU/mg protein and a Km for fructose 6-phosphate of 40 microM. Induction of citric acid accumulation (acidogenesis) in A. niger by cultivation on high concentrations of sucrose, or replacement on 14% (w/v) sucrose correlated with an increase in the intracellular concentration of Fru-2,6-P2. A similar correlation was obtained when A. niger was cultivated on different carbon sources, which induced different rates of acidogenesis. The increase in Fru-2,6-P2 during transfer to 14% (w/v) sucrose was not correlated with the behaviour of mycelial concentrations of cyclic AMP, a potential regulator of Fru-2,6-P2 formation in other organisms, nor with that of Fru-6-P and ATP, the precursors of its formation. The extracellular addition of cyclic AMP and theophylline, an inhibitor of cellular cyclic AMP breakdown, increased both Fru-2,6-P2 concentration and acidogenesis in mycelia cultivated in 1% (w/v) sucrose medium. It is concluded that Fru-2,6-P2 controls citric acid accumulation by enabling increased rates of glucolysis, a prerequisite to acidogenesis.
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