Mutations in phosphofructokinases alter the control characteristics of glycolysis in vivo in Saccharomyces cerevisiae

Ethanol and CO 2 production from gluecose by non‐proliferating suspensions of aerobicaly‐grown, glucose‐derepressed wild‐type Sacharomyces cerevisiae is inhibited by O 2 ; monitoring by mass spectrometry provides a direct method for measurement of the Pasteur effect. Under aerobic conditons, that part of the CO 2 evolved equivalent to the O 2 consumed, is produced by respiration: subtraction of this respiratory CO 2 from the total gives, CO 2 produced by aerobic glycolysis. Pasteur quotients (anaerobic CO 2 /aerobic glycolytic CO 2 ) were within the range 1.2 to 3.0. The Pasteur effect was not observed in the presence of carbonyl cyanid m ‐chlorophenylhydrazone, an uncoupler of mitochondrial energy metabolism, or in a ρ cytoplasmic petite mutant. A ‘non‐allosteric’ mutant with an altered regulatory subunit of phosphofructokinase showed no Pasteur effect. Strains bearing a nonsense mutation pfk1 in the catalytic subnit of soluble phosphofructokinase (PFKI) also showed no Pasteur effect; the residual fermentative activity of this strain was dependent on PFKII, the particulate phosphofructokinase. A double mutant lacking both PFKI and glucose‐6‐phosphat dehydrogenase showed similar characteristics to those of the single pfk1 mutant; this indicates that the hexose monophosphate shunt is not acting to bypass the phosphofructokinase block. A ‘hyper‐allosteric’ mutant altered in the regulatory subunit encoded by the gene PFK2 showed characteristics of glucose fermentation and ethanol oxidation very similar to those of wild‐type organisms. These results indicate that either of the two phosphofructokinases can cary out glycolysis.