Mitochondrial respiratory mutants of Saccharomyces cerevisiae accumulate glycogen and readily mobilize it in a glucose-depleted medium.
Mutant strains of Saccharomyces cerevisiae defective in respiration have been reported to be unable to store glycogen, as revealed by the iodine-staining method. In this report, it is shown that in contrast to this claim, mitochondrial respiratory mutants accumulated even more glycogen than wild-type cells during the fermentative growth on glucose. However, as soon as glucose was exhausted in the medium, these mutants readily and completely mobilized their glycogen content, contrary to wild-type cells which only transiently degraded this polymer. The mobilization of glycogen was a specific trait resulting from a defect in mitochondrial function that could not be suppressed by mutations in the cAMP- and Pho85 protein kinase-dependent nutrient-sensing pathways, and by other mutations which favour glycogen synthesis. To account for this mobilization, it was found that respiration-defective cells not only contained a less active glycogen synthase, but also a more active glycogen phosphorylase. Since glucose 6-phosphate (Glc6P) is a potent inhibitor of the phosphorylation and an activator of the dephosphorylation processes of glycogen synthase and glycogen phosphorylase, it is suggested that the drop in Glc6P observed at the onset of glucose depletion in respiration-deficient cells triggers this rapid and sustained glycogen mobilization. It is also proposed that this degradation provides the energy for the viability of respiratory mutants in glucose-starved medium.
Enjalbert
Brice
B
Centre de Bioingénierie Gilbert Durand, UMR-CNRS 5504, UR-INRA 792, Département de Génie Biochimique et Alimentaire, Complexe Scientifique de Rangueil, 31077 Toulouse, France1.
Parrou
Jean Luc
JL
Centre de Bioingénierie Gilbert Durand, UMR-CNRS 5504, UR-INRA 792, Département de Génie Biochimique et Alimentaire, Complexe Scientifique de Rangueil, 31077 Toulouse, France1.
Vincent
Olivier
O
Centre de Bioingénierie Gilbert Durand, UMR-CNRS 5504, UR-INRA 792, Département de Génie Biochimique et Alimentaire, Complexe Scientifique de Rangueil, 31077 Toulouse, France1.
François
Jean
J
Centre de Bioingénierie Gilbert Durand, UMR-CNRS 5504, UR-INRA 792, Département de Génie Biochimique et Alimentaire, Complexe Scientifique de Rangueil, 31077 Toulouse, France1.
D017920:Antiporters / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins; D005800:Genes, Fungal; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D007455:Iodine / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009154:Mutation; D010101:Oxygen Consumption / Q000235:genetics* / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013194:Staining and Labeling / Q000379:methods; D013997:Time Factors; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
D017920:Antiporters; D003470:Culture Media; D005656:Fungal Proteins; D009004:Monosaccharide Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; C111261:glucose 6-phosphate(transporter); D006003:Glycogen; D007455:Iodine; D018844:Cyclin-Dependent Kinases; C058605:PHO85 protein, S cerevisiae; D018631:ras Proteins; D005947:Glucose