Chemostat cultures of an aerobic fermenting yeast (Saccharomyces cerevisiae) and an aerobic respiring yeast (Kluyveromyces fragilis) were grown under dual C + N limitation in an isothermal reaction calorimeter. The dual limitations resulted in uncoupled oxidn. of part of the glucose, which enabled the culture to adapt the ratio of N/C consumption rates precisely to the N/C ratio that was fed into the calorimeter. This conclusion was reached based on the calorimetric measurements, which reflect uncoupled respiration conspicuously as abnormal heat yields or ratios of heat release per biomass grown. [on SciFinder (R)]