Changes in the concentration of fructose 2,6-bisphosphate in Aspergillus niger during stimulation of acidogenesis by elevated sucrose concentration.
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.
Kubicek-Pranz
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Abteilung für Mikrobielle Biochemie, Institut für Biochemische Technologie und Mikrobiologie, Wien, Austria.
Mozelt
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Rohr
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Kubicek
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D000255:Adenosine Triphosphate / Q000378:metabolism; D001234:Aspergillus niger / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D002951:Citrates / Q000378:metabolism*; D019343:Citric Acid; D003470:Culture Media; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D005635:Fructosediphosphates / Q000096:biosynthesis / Q000378:metabolism*; D005636:Fructosephosphates / Q000378:metabolism; D006019:Glycolysis; D006598:Hexosediphosphates / Q000378:metabolism*; D025481:Phosphofructokinase-2; D010770:Phosphotransferases / Q000378:metabolism; D013395:Sucrose / Q000008:administration & dosage* / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology
D002951:Citrates; D003470:Culture Media; D005635:Fructosediphosphates; D005636:Fructosephosphates; D006598:Hexosediphosphates; D019343:Citric Acid; D013395:Sucrose; C027618:fructose-6-phosphate; C027652:fructose 2,6-diphosphate; D000255:Adenosine Triphosphate; D013806:Theophylline; D000242:Cyclic AMP; D010770:Phosphotransferases; D025481:Phosphofructokinase-2