Aerobic adaptation in yeast. III. Changes in metabolic intermediates during anaerobic–aerobic transitions in exponentially growing cultures

The changes in mechanism of control and in the mode of metabolism which yeast cells undergo when an anaerobic–aerobic transition is imposed on them has received much attention. One experimental approach to this type of investigation has been a step-down transition. The data from our experiments (cf. papers I and II of this series) has shown that this model is too complex to arrive at meaningful interpretation. We therefore repeated these measurements of glycolytic and citric acid cycle metabolites in cells growing on either glucose or galactose media and exposed to exponential N2 → O2 transitions. This type of experiment is designed to examine directly the effect of oxygen challenge. Interpretation of this new data shows that the major metabolic control operating in the two hexose cultures are different and suggests that adenine nucleotide controls glucose cells whereas galactose cell metabolism is controlled by the NAD/NADH balance. This concept is discussed.