Influence of glucose on the deoxyglucose metabolism in S cerevisiae: detection and identification of deoxyglucose and trehalose derivatives by 1H- and 13C-NMR spectroscopy

Detection of modifications in the glucose metabolism induced by genetic mutations in Saccharomyces cerevisiae by 13C- and H-NMR spectroscopy

NMR spectroscopy may offer a suitable technique to characterize the glucose metabolism in response to genetic mutations in cells. The effects of various genetic modifications in Saccharomyces cerevisiae yeast were investigated using 13C- and 1H-NMR spectroscopy associated with biochemical techniques. Cells were incubated with [1-13C]glucose in order to study glucose consumption and the formation of various end-products (ethanol, trehalose, glycerol, glutamate and amino acids) as a function of time. Two types of genetic modifications were studied in S. cerevisiae. A genetic modification deleted the N-terminal part of the TFC7 protein which is the smallest subunit (tau55) of the TFIIIC transcription factor. One secondary effect of this mutation was a large deletion of mitochondrial DNA giving the rho-phenotype. The other genetic modification corresponded to the disruption of the HUF gene; the mutated cells were rho+ like the reference strain. Both mutations increase the glycolysis rate and glycerol synthesis and decrease trehalose production. The most modified cells, which contain both TFC7 deletion and HUF gene disruption, utilize glucose in the most extreme manner as in these cells the largest production of the two glycolytic products (ethanol and glycerol) and the smallest trehalose formation occur. The HUF gene disruption serves as a positive modulator of glycolysis and respiration. However, the TFC7 deletion, associated with the phenotype rho-, induces the most damage in the cellular function, dramatically altering the behaviour of the Krebs cycle. The cycle becomes blocked at the level of 2-oxoglutarate, detected by a characteristic pattern of the 13C-NMR glutamate spectra. These NMR spectra corroborate the phenotypic data, the rho-phenotype corresponding to deletions of mitochondria DNA which block all mitochondria protein synthesis and render the cells unable to derive energy from respiration. Moreover, as a consequence of the Krebs cycle blocking, alanine formation is also observed.

Effects of amphotericin B on glucose metabolism in Candida albicans blastospores evidenced by 13C NMR

Candida albicans blastospores harvested from 8- (exponential phase) or 48-h (stationary phase) cultures were incubated with 60 x 10(-3)M [1-(13)C]glucose with or without 10(-4)M amphotericin B (AmB). The utilization of [1-(13)C]glucose was monitored by in vivo 13C NMR under anaerobiosis. With exponential phase cells, in the presence of AmB, the consumption of glucose and the production of ethanol, trehalose, and glycerol continuously decreased with time, and after 25 min, the metabolism was blocked. On stationary phase cells AmB had almost no effect on glucose metabolism. Comparison with previous experiments evidenced that AmB induced first K+ leakage, then acidification, and finally a stop of the metabolism. In parallel, in vitro 13C NMR spectra were performed on supernatants and cell-free extracts of yeast suspension incubated under the same conditions. For both exponential and stationary phase cells, AmB induced an increase in the membrane permeability to glycerol; no change was observed for the other metabolites.

A novel approach for investigating reaction mechanisms in cells. Mechanism of deoxy-trehalose synthesis in Saccharomyces cerevisiae studied by 1H-NMR spectroscopy

A new approach is proposed for investigating the mechanism of metabolite synthesis in cells. This method, based on the competition between various substrates, allows the flux along a pathway, which is normally independent of the concentration of the corresponding precursor in the external medium, to be divided into partial fluxes. In particular, the mechanism deoxy-trehalose synthesis in glucose-grown repressed Saccharomyces cerevisiae was studied, by 1H-NMR spectroscopy, using the competition between 2-deoxy-D-glucose (dGlc) and 2-fluoro-deoxy-D-glucose (FdGlc) with respect to hexokinase. S. cerevisiae cells, suspended in a standard pyrophosphate medium containing about 5 x 10(7) cells/ml, were incubated with 30 mM glucose and various concentrations of dGlc and FdGlc. Apart from dGlc6P and FdGlc6P, trehalose and the dissacharides relative to dGlc, i.e. dideoxy-trehalose (dGlc-dGlc) and deoxytrehalose (dGlc-Glc), are observed while their analogues relative to FdGlc (FdGlc-FdGlc, FdGlc-Glc) are surprisingly absent. For the same external concentration of dGlc and FdGlc, the internal concentration of FdGlc6P is about three times larger than that of dGlc6P. The ratio of the FdGlc6P and dGlc6P concentrations is independent of the incubation times and proportional to the FdGlc and dGlc concentrations in the suspension. The dGlc6P concentration can thus be reduced at will by increasing the [FdGlc]/[dGlc] ratio. Under these conditions, the dGlc-Glc concentration was found to vary linearly with that of dGlc6P. The present data clearly show that deoxy-trehalose is not synthesized from UDP-dGlc and Glc6P but from UDP-Glc and dGlc6P. This conclusion was also confirmed by an experiment in which S. cerevisiae cells were previously charged with dGlc6P and then incubated with glucose.

Reciprocal effects of 2-fluoro-2-deoxy-D-glucose and glucose on their metabolism in Saccharomyces cerevisiae studied by multi-nuclear NMR spectroscopy

The effects of various concentrations of 2-fluoro-2-deoxy-D-glucose (FDG) on the aerobic metabolism of glucose and the reciprocal effect of glucose on the metabolism of FDG in glucose-grown repressed Saccharomyces cerevisiae cells were studied at 30 degrees C in a standard pyrophosphate medium containing 5 x 10(7) cells/ml by 1H-, 19F-, 31P-NMR and biochemical techniques. The glucose consumption rate is reduced by about 57% and 71% in the presence of 5 mM FDG and 10 mM FDG respectively. Under the same conditions, the ethanol production rate also decreases about 54% and 68%, respectively. When FDG is the unique carbon source, the alpha- and beta-anomers of 2-fluoro-2-deoxy-D-glucose-6-phosphate (FDG6P) and a much smaller quantity of 2-fluoro-2-deoxy-gluconic acid (FDGA) were observed. The quantities of alpha- and beta-FDG6P reach their maximum values within 1 h of incubation and then decrease continuously. In contrast, Glc favors the consumption of FDG and the synthesis of FDG6P and uridine-5'-diphosphate fluorodeoxy-glucose (UDP-FDG). In the presence of Glc, FDG6P reaches a plateau after 1 h or 2 h of incubation while UDP-FDG increases regularly with time. Apart from trehalose, no other disaccharide such as fluoro-dideoxy-trehalose (FDG-FDG) or fluoro-deoxy-trehalose (FDG-Glc) were observed. Thus, in contrast to UDP-Glc, UDP-DG, Glc6P and DG6P, UDP-FDG and FDG6P are not good substrates for trehalose-6-P synthetase.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-cooperative effects of glucose and 2-deoxyglucose on their metabolism in Saccharomyces cerevisiae studied by 1H-NMR and 13C-NMR spectroscopy

The reciprocal effects of 2-deoxy-D-glucose (dGlc) and glucose (Glc) on the aerobic metabolism of Glc and dGlc in Glc-grown repressed Saccharomyces cerevisiae were studied at 30 degrees C in a standard pyrophosphate medium containing about 4.5 x 10(7) cells/ml. 1H-, 13C-NMR and biochemical techniques were used for quantitative evaluation of Glc and dGlc metabolites. The detection of intracellular dGlc and the determination of the intracellular dGlc6P/dGlc ratio were realised using [1-13C]dGlc and 13C-NMR spectroscopy. The rates of Glc consumption in the absence and in the presence of 5 mM dGlc and 20 mM dGlc were 29 +/- 0.03 mM/min (n = 3), 16 +/- 0.02 mM/min (n = 3), and 0.08 +/- 0.01 mM/min (n = 3), respectively. This means that the Glc consumption is reduced about 41% and 70% in the presence of 5 mM and 20 mM dGlc, respectively. When dGlc is the unique carbon source, only alpha and beta anomers of dGlc6P were formed. Their quantities are equivalent and reach the maximum values within 1 h of incubation and then decrease gradually. By contrast, Glc favours the consumption of dGlc and the synthesis of dGlc6P, dideoxy-trehalose (dGlc-dGlc), deoxy-trehalose (dGlc-Glc). In the presence of Glc, dGlc6P reaches a plateau after 1 h or 2 h of incubation while the quantities of trehalose (Glc-Glc), dGlc-dGlc, dGlc-Glc, which are small at 1 h, rapidly increase with time. The reasons why dGlc and Glc exert opposite effects on their metabolism are discussed. The production of Glc-Glc decreases with increasing the external dGlc concentration or the dGlc/Glc ratio. The effect of dGlc on the biosynthesis of Glc-Glc can be explained by the competition of dGlc and Glc with respect to hexokinase. Although Glc favours the synthesis of dGlc6P, the maximum concentration of dGlc6P shows little dependence on the external dGlc concentration as long as glucose is not exhausted. The internal dGlc6P/dGlc ratio at equilibrium, about 4.7 +/- 0.7, is also found to be independent of the dGlc concentration in the suspension. Only a small fraction of dGlc6P disappears to give rise to the formation of dGlc-dGlc and dGlc-Glc. At equilibrium the inverse reaction from dGlc6P to dGlc may be important to compensate for the fast reaction of dGlc phosphorylation by hexokinase. At least nine series of experiments were conducted and showed that, in pyrophosphate media and for incubation times less than 4 h, dGlc-dGlc was not observed in the absence of Glc.(ABSTRACT TRUNCATED AT 400 WORDS)