Summary: The methylotrophic yeast sp. 2201 was grown in carbon-limited chemostat cultures with glucose and/or methanol as the carbon sources, to investigate the regulation of the synthesis of enzymes involved in the tricarboxylic acid (TCA) cycle and the electron transport chain.

Except for malate dehydrogenase, enzymes of the TCA cycle were repressed during growth with methanol to specific activities of 20-40% of those found in cells growing under identical growth conditions but with glucose as the carbon source. In methanol-grown cells, the specific activities of the enzymes of the respiratory chain were also repressed compared to cells grown with glucose [60-70% for NADH: cytochrome (cyt ) oxidoreductase and cyt oxidase; approximately 40% for succinate:cyt oxidoreductase]. The measurement of cytochrome oxidized-minus-reduced spectra was impossible in methanol-grown cells because of interference of the chromophoric group of the peroxisomal enzyme alcohol oxidase under these growth conditions. The relative cytochrome content of mitochondria from methanol-grown cells, separated from peroxisomes by density gradient centrifugation, was significantly lower (cyt :cyt :cyt = 1:1.24:0.86) than in mitochondria from glucose-grown cells (cyt : cyt :cyt = 1:1.27:2.20). The results are discussed with respect to the generation of energy for biosynthesis during growth with glucose and/or methanol.


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