2Bach Institute of Biochemistry, Russian Academy of Sciences, Leninsky pr. 33, 119071 Moscow, Russia; E-mail: email@example.com
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Received March 24, 2005
The rate of endogenous respiration of Saccharomyces cerevisiae cells incubated at 0°C under aerobic conditions in the absence of exogenous substrates decreased exponentially with a half-period of about 5 h when measured at 30°C. This was associated with an indirectly shown decrease in the level of oxaloacetate in the mitochondria in situ. The initial concentration of oxaloacetate significantly decreased the activity of succinate dehydrogenase. The rate of cell respiration in the presence of acetate and other exogenous substrates producing acetyl-CoA in mitochondria also decreased, whereas the respiration rate on succinate increased. These changes were accompanied by an at least threefold increase in the L-malate concentration in the cells within 24 h. It is suggested that the increase in the L-malate level in the cells and the concurrent decrease in the oxaloacetate level in the mitochondria should be associated with a deceleration at 0°C of the transport of endogenous respiration substrates from the cytosol into the mitochondria. This deceleration is likely to be caused by a high Arrhenius activation energy specific for transporters. The physiological significance of L-malate in regulation of the S. cerevisiae cell respiration is discussed.
KEY WORDS: endogenous cell respiration, low temperature, L-malate, oxaloacetate, malonate, transporters, Saccharomyces cerevisiae