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

Abstract

Ethanol and CO₂ production from gluecose by non-proliferating suspensions of aerobicaly-grown, glucose-derepressed wild-type Sacharomyces cerevisiae is inhibited by O₂; monitoring by mass spectrometry provides a direct method for measurement of the Pasteur effect. Under aerobic conditons, that part of the CO₂ evolved equivalent to the O₂ consumed, is produced by respiration: subtraction of this respiratory CO₂ from the total gives, CO₂ produced by aerobic glycolysis. Pasteur quotients (anaerobic CO₂/aerobic glycolytic CO₂) 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.