D. Michaljaničová

Uptake of trehalose by Saccharomyces cerevisiae.

Trehalose, a storage sugar of bakers yeast, is known not to be metabolized when added to a cell suspension in water or a growth medium and to support growth only after a lag of about 10 h. However, it was transported into cells by at least two transport systems, the uptake being active, with a pH optimum at 5.5. There was no stoicheiometry with the shift of protons into cells observed at high trehalose concentrations. Trehalose remained intact in cells and was not appreciably lost to a trehalose-free medium. The uptake systems were present directly after growth on glucose, then decayed with a half-life of about 25 min but could be reactivated by aerobic incubation with trehalose, maltose, alpha-methyl-D-glucoside, glucose or ethanol. The uptake systems thus induced were different as revealed by competition experiments. At least one of the systems for trehalose uptake showed cooperative kinetics. Comparative anaysis with other disaccharides indicated the existence in Saccharomyces cerevisiae, after induction with trehalose, of at least four systems for the uptake of alpha-methyl-D-glucoside, four systems for maltose, together with the two for trehalose, variously shared by the sugars, the total of alpha-glucoside-transporting systems being five.

Transport of 4-deoxy- and 6-deoxy-D-glucose in baker's yeast

Tritium-labelled 4-deoxy-D-glucose (4-dglc) and 6-deoxy-D-glucose (6-dglc) were prepared by catalytic hydrogenolysis of the corresponding deoxyiodo derivatives with gaseous tritium. The two sugars are transported intoSaccharomyces cerevisiae by both the constitutive glucose and the inducible galactose carrier. Uranyl ions are powerful inhibitors. The pH optimum in uninduced cells lies at 5.5 for both sugars, the apparent activation energies (between 15 and 35°C) are 25.1 kJ/mol and 16.5 kJ/mol, respectively. The steady-state intracellular concentration of both sugars is less than the extracellular one (no uphill transport). Neither of them is a substrate of yeast hexokinase. 4-Deoxy-D-glucose undergoes a dinitrophenol-sensitive conversion to an unknown metabolite which is not phosphorylated and may represent one of its oxidation products.

Transport kinetics of 6-deoxy-D-glucose inCandida parapsilosis

The strictly aerobic yeastCandida parapsilosis transports the nonmetabolizable monosaccharide 6-deoxy-D-glucose by an active process (inhibition by 2.4-dinitrophenol and other uncouplers but not by iodoacetamide), the accumulation ratio decreasing with increasing substrate concentration. Measured accumulation ratios are in agreement with those predicted from kinetic constants for influx and efflux. Energy for transport is probably required in the translocation step. The maximum rate is temperature-dependent with a transition point at 21 °C. the accumulation ratio is not, The uptake is most active at pH 4.5–8.5. It appears not to involve stoichiometric proton symport. The transport system is shared by D-glucose, D-mannose, D-galactose and possibly maltose but not by fructose, sucrose or pentoses. The apparent half-life of the transport system was 3.5–4 h.

Suspension density and accumulation ratio of sugars and amino acids in yeasts

Suspension density has a pronounced effect on the transport parameters of monosaccharides, disaccharides and amino acids in all ycast species tested. InLodderomyces elongisporus, the accumulation ratio of 6-deoxy-D-glucose, a nonmetabolized sugar, was as high as 560: 1 at 0.5 mg dry mass per mL but only 10: 1 at 50 mg dry mass per mL. In the low-density range, the temperature optimum was very pronounced (at about 40 °C) and the pH optimum was very clear at pH 4.6. Iodoacetamide (0.5 mmol/L), 2,4-dinitrophenol (0.5 mmol/L), uranyl ions (0.5 mmol/L) and 2-deoxy-D-glucose (10 mmol/L) depressed the accumulation in the low-density range by 42, 97, 96 and 98 %, respectively. Preincubation with 1% sucrose and 1% L-fructose stimulated subsequent accumulation by 40 and 105%, respectively. In the high-density range, there was a poorly pronounced temperature optimum, no pH optimum and little effects of inhibitors except 2,4-dinitrophenol and 2-deoxy-D-glucose which inhibited by 68 and 89% respectively. No stimulation by preincubation with sugars was observed. There was a difference of 0.3 pH units in the intracellular pH of high-density and low-density cells and the membrane potential was -31 mV and -78 mV, respectively, which could not account for the differences in accumulation. However, there was a fine correlation between this accumulation ratio and the activity of the plasma membrane H+ATPase.

Maltotriose transport and utilization in Baker’s and Brewer’s yeast

AbstractMaltotriose is metabolized by baker’s and brewer’s yeast only oxidatively, with a respiratory quotient of 1.0, the

Densitometry of yeast cells and protoplasts during sugar uptake.

Q_{CO_2 } ^{Ar}

Membrane mutation affecting energy-linked functions in Escherichia coli K 12.

being, depending on the strain used, 0–11, as compared with