The whi2 mutation in S. cerevisiae allows mutant cells to grow with a higher specific rate and at smaller cell sizes at the onset of EtOH metab. in diauxic growth. S. cerevisiae Whi2+ and whi2 were cultivated in aerobic and anaerobic batch cultures in the BSC 81 calorimeter, with glucose and galactose as substrates. The mutation was obsd. only during fully oxidative growth; anaerobic or oxidoreductive growth did not result in the expression of the gene. The heat data confirmed a metabolic difference in the 2 strains at the onset of the diauxic lag phase. Mutant whi2 cells have a more efficient oxidative metab. than parent Whi2+ cells; heat dissipation during oxidative growth is 5 kJ/g lower for whi2 cells. The higher specific growth rate and the more efficient metab. of whi2 cells undergoing fully oxidative growth can be explained in the context of a biol. limited respiratory capacity in Saccharomyces-type yeasts. [on SciFinder (R)]