We have re-assessed the hypothesis that an accumulation of intracellular glycerol triggers the accumulation of citric acid by by inhibiting the activity of the mitochondrial NADP-dependent isocitrate dehydrogenase isoenzyme. To this end, we have incubated mycelia of 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-C]citrate from the medium nor the rate of the subsequent release of CO 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 CO from exogenously added [1,5-C]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 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.


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