Studies of Anaerobic and Aerobic Glycolysis in Saccharomyces cerevisiae

Glucose metabolism was followed in suspensions of Saccharomyces cerevisiae by using ¹³C NMR and ¹⁴C radioactive labeling techniques and by Warburg manometer experiments. These experiments were performed for cells grown with various carbon sources in the growth medium, so as to evaluate the effect of catabolite repression. The rate of glucose utilization was most conveniently determined by the ¹³C NMR experiments, which measured the concentration of [l-¹³C]glucose, whereas the distribution of end products was determined from the ¹³C and the ¹⁴C experiments. By combining these measurements the flows into the various pathways that contribute to glucose catabolism were estimated, and the effect of oxygen upon glucose catabolism was evaluated. From these measurements, the Pasteur quotient (PQ) for glucose catabolism was calculated to be 2.95 for acetate-grown cells and 1.89 for cells grown on glucose into saturation. The Warburg experiments provided an independent estimate of glucose catabolism. The PQ estimated from Warburg experiments was 2.9 for acetate-grown cells in excellent agreement with the labeled carbon experiments and 4.6 for cells grown into saturation, which did not agree. Possible explanations of these differences are discussed. From these data an estimate is obtained of the net flow through the Embden-Meyerhof-Parnas pathway. The backward flow through fructose-1,6-bisphosphatase (Fru-1,6-P₂-ase) was calculated from the “scrambling” of the ¹³C label of [1-¹³C] glucose into the C₁ and C₆ positions of trehalose. Combining these data allowed us to calculate the net flux through phosphofructokinase (PFK). For acetate-grown cells we found that the relative flow through PFK is a factor of 1.7 faster anaerobically than aerobically. This change in the rate of PFK is less than the change of 2.9 in the overall rate of glucose catabolism in part because of different flows into storage compounds and in part because the Fru-1,6-P₂-ase flux was approximately 40% of the PFK flux under aerobic conditions and negligible anaerobically.