Metabolism of 2-deoxy-D-glucose in Baker's yeast. V. Formation of 2-deoxy- , '-trehalose

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.

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)

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

The metabolism of 2-deoxy-D-glucose (DG) in glucose grown repressed Saccharomyces cerevisiae cells was studied in the absence and presence of glucose (Glc) at 30 degrees C in a standard pyrophosphate medium containing 4.5 x 10(7) cells/ml. 1H- and 13C-NMR spectroscopy were successfully used to distinguish and identify several derivatives of DG and trehalose. Using [1-13C]DG, alpha- and beta-DG, alpha- and beta-DG6P, dideoxy-trehalose (DG-DG) and deoxy-trehalose (DG-Glc) can be simultaneously observed in the intracellular medium. The [DG6P]/[DG] ratio is about 5-6. The results seem to indicate the existence of an equilibrium between DG and DG6P, which limits the production of DG6P in cells. Glucose was found to exert a great influence on the metabolism of DG. It favours the formation of DG-DG and DG-Glc.

Enzyme-catalyzed organic synthesis of sucrose and trehalose with in situ regeneration of UDP-glucose

This paper describes cell-free enzymatic syntheses of sucrose and trehalose using partially-purified preparations of sucrose and trehalose synthetase. The coupling of the regeneration of uridine-5'-diphosphoglucose (UDP-Glc) with synthesis of the disaccharide offers a practical route to millimol quantities of these carbohydrates. The syntheses used pyruvate kinase, UDP-Glc pyrophosphorylase, and inorganic pyrophosphatase, and the regenerated UDP-Glc was cycled approximately 10 times.

Transglycosylic reactions of deoxysugars. Biosynthesis of deoxy analogues of starch

The biosynthesis of starch was investigated in the reaction catalyzed by plant alpha(1 leads to 4)-glucan phosphorylase using alpha-D-glucopyranosyl phosphate and its deoxy analogues as substrates. It was found that the hydroxyl groups at the positions C-2, C-3, C-4 and C-6 in the glucose moiety of the molecule of alpha-D-glucopyranosyl phosphate are not essential for its substrate properties in the transglycosylic reaction. The affinity of plant (alpha(1 leads to 4)-glucan phosphorylase and the rate of hexose incorporation into alpha(1 leads to 4)-glucan decreases in the following sequence: alpha-D-glucopyranosyl phos-phosphate, 2-deoxy-, 6-deoxy, 4-deoxy, and 3-deoxy-alpha-D-glucopyranosyl phosphate. The deoxyglucosyl analogues of alpha-D-glucosylpyranosyl phosphate act as competitive inhibitors on the elongation reaction of the alpha(1 leads to 4) chains of starch. It was found that more than one residue of 2-deoxy-D-glucose or 6-deoxy-D-glucose can be incorporated into the nonreducing terminus of alpha(1 leads to 4)-glucan chains of starch.

Transglycosylic reactions of nucleotides of deoxy sugars. Biosynthesis of deoxy analogues of alpha,alpha'-trehalose

The biosynthesis of alpha,alpha'-trehalose was investigated in a reaction catalyzed with yeast UDP-Glc :glucose-6-phosphate 1-glucosyl transferase. It was revealed that the hydroxyls at positions C-2, C-3, C-4 and C-6 are not essential for preserving its substrate properties in this reaction. The affinity of the enzyme and the rate of hexose incorporation into trehalose decreases in following sequence: UDP-glucose, UDP-2-deoxy-D-glucose, UDP-6-deoxy-d-glucose, UDP-4-deoxy-D-glucose and UDP-3-deoxy-D-glucose.

Lysis of Saccharomyces cerevisiae with 2-deoxy-2-fluoro-D-glucose, an inhibitor of the cell wall glucan synthesis

The effect of a synthetic glucose analogue, 2-deoxy-2-fluoro-d-glucose (FG) on growth and glucose metabolism of Saccharomyces cerevisiae was studied. The addition of FG (0.005-0.05%) to a 2% glucose medium resulted in reduction of the initial growth rate and, after several hours, in a complete cessation of the culture growth. These two events were due to extensive lysis of the population which continued long after the period when no more growth was recorded. Electron microscope examination of lysed cells showed that the lysis was a consequence of a dissolution of the cell walls. FG inhibited to a similar extent the initial growth rate and the incorporation of radioactivity from labeled glucose into growing population. The inhibition of radioactivity incorporation from glucose by growing protoplasts was much less. The yeast was found to be extremely FG sensitive whenever the synthesis of new cell wall material was involved. All observations imply that FG interferes mainly with the cell wall formation of S. cerevisiae. A comparison of the FG effects on metabolic activity of protoplasts, simultaneous secretion of mannan-proteins into the growth medium, and the formation of glucan fibrils on the surface of protoplasts demonstrated that the cell wall glucan synthesis is the most FG-sensitive process and evidently the growth-limiting factor in intact cells. FG-resistant cells were selected during growth experiments. They exhibited an altered mode of cell division when grown in the presence of FG.