Glycerol is not an inhibitor of mitochondrial citrate oxidation by Aspergillus niger

We have re-assessed the hypothesis that an accumulation of intracellular glycerol triggers the accumulation of citric acid by Aspergillus niger by inhibiting the activity of the mitochondrial NADP-dependent isocitrate dehydrogenase isoenzyme. To this end, we have incubated mycelia of A. niger with 0...

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Bibliographic Details
Published in:Microbiology (Society for General Microbiology) 1996-10, Vol.142 (10), p.2937-2942
Main Authors: Arisan-Atac, I, Kubicek, C.P
Format: Article
Language:English
Subjects:
Aspergillus niger - enzymology
Aspergillus niger - metabolism
Biological and medical sciences
Biological Sciences
Biological Transport - drug effects
Carbon Dioxide - metabolism
Cell Fractionation
Citric Acid - metabolism
Fundamental and applied biological sciences. Psychology
Glycerol - analysis
Glycerol - pharmacology
Growth, nutrition, metabolism, transports, enzymes. Molecular biology
Isocitrate Dehydrogenase - metabolism
Microbiology
Mitochondria - enzymology
Mitochondria - metabolism
Mycology
Oxidation-Reduction
plant biochemistry
plant physiology
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Summary:We have re-assessed the hypothesis that an accumulation of intracellular glycerol triggers the accumulation of citric acid by Aspergillus niger by inhibiting the activity of the mitochondrial NADP-dependent isocitrate dehydrogenase isoenzyme. To this end, we have incubated mycelia of A. niger with 0.5 M glycerol, which resulted in a maximal intracellular glycerol pool level of 0.92 M, comparable to that determined during the early phase of citrate accumulation. This addition affected neither the uptake of [1,5-14C]citrate from the medium nor the rate of the subsequent release of 14CO2 by the mycelia, indicating no effect on citrate oxidation. Mitochondria isolated from mycelia previously loaded with 0.5 M glycerol contained 8% of the total mycelial glycerol. They released 14CO2 from exogenously added [1.5-14C]citrate at the same rate as mitochondria isolated from mycelia not loaded with 0.5 M glycerol. The addition of glycerol had no effect on the activity of the purified NADP-specific isocitrate dehydrogenase, but appeared to inhibit the activity in crude cell-free extracts of A. niger. We conclude that the intracellular accumulation of glycerol does not affect the rate of mitochondrial citrate oxidation and is therefore In contrast to previous claims not a trigger of citrate accumulation.
ISSN:1350-0872
1465-2080
DOI:10.1099/13500872-142-10-2937