Changes in the intracellular concentrations of adenosine phosphates and nicotinamide nucleotides during the aerobic growth cycle of yeast on different carbon sources.

1. Methods for the quantitative extraction of adenosine phosphates and nicotinamide nucleotides from yeast cells are described. 2. The intracellular concentrations of adenosine phosphates and nicotinamide nucleotides were measured during the aerobic growth cycle of yeast on glucose and galactose. 3. When sugars were still present in the media the intracellular concentrations of NADH and AMP were in general higher in glucose- than in galactose-grown cells, whereas ADP concentration was always lower in glucose-grown cells. 4. The adenylate-kinase reaction was found to be far from equilibrium in the glucose-grown cells and when glucose was still present in the growth medium. 5. The significance of the changes in the intracellular concentrations of adenosine phosphates and nicotinamide nucleotides observed during growth on either sugar is discussed in relation to the metabolism and growth of the cells. 6. The differences observed in the concentrations of these cofactors in glucose- and galactose-grown cells are also discussed in relation to the type of metabolism of these cells. Control of glycolysis at the level of phosphofructokinase in galactose-grown cells and at the level of phosphoglycerate kinase in glucose-grown cells is suggested. 7. ADP is suggested to be the inducer of formation of respiratory enzymes.