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Inhibition of fungal NADP + ‐isocitrate dehydrogenase by citric acid
Author(s) -
Agrawal P. K.,
Bhatt C. S.,
Viswanathan L.
Publication year - 1983
Publication title -
zeitschrift für allgemeine mikrobiologie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.58
H-Index - 54
eISSN - 1521-4028
pISSN - 0044-2208
DOI - 10.1002/jobm.19830230613
Subject(s) - citric acid , aspergillus niger , isocitrate dehydrogenase , mycelium , dehydrogenase , enzyme , chemistry , biochemistry , enzyme assay , citric acid cycle , nuclear chemistry , biology , botany
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.