title: Inhibition of fungal NADP+-isocitrate dehydrogenase by citric acid.
abstract: The variations observed during earlier studies in the activity of NADP+-isocitrate dehydrogenase (EC. 1.1.1.42) in a strain of Aspergillus niger were found to be related to the extent of washing of mycelium. As a result the mycelium washed four times with phosphate buffer (0.05 M, pH 7.5), the enzyme activity present in 4 and 8 days old fungal mycelia increased five- and two-fold, respectively. In vivo studies showed a complete loss of enzyme activity in mycelia resuspended in HCl-KCl buffer (0.02 M, pH 2.2) containing citric acid (13 mM or more). The in vitro studies revealed 50% loss of enzyme activity in presence of 3.6 to 5.2 mM citric acid. However, in case of Aspergillus niger ATCC 1015, which produced less citric acid than the above strain, a much higher citric acid concentration (13 to 26 mM) was required to cause 50% loss of enzyme activity. These findings suggest a correlation between citric acid inhibition of NADP+-isocitrate dehydrogenase and the ability of A. niger to accumulate citric acid in the medium.
mesh_terms: D001234:Aspergillus niger / Q000187:drug effects* / Q000201:enzymology; D002951:Citrates / Q000494:pharmacology*; D019343:Citric Acid; D003470:Culture Media; D004794:Enzyme Repression; D007521:Isocitrate Dehydrogenase / Q000096:biosynthesis*
chemical_list: D002951:Citrates; D003470:Culture Media; D019343:Citric Acid; D007521:Isocitrate Dehydrogenase; C039355:isocitrate dehydrogenase (NADP+)