Accumulation of trehalose and sucrose in relation to the metabolism of alpha-glucosides in yeasts of defined genotype

Kinetics of active sucrose transport in Saccharomyces cerevisiae

The kinetic analysis of active sucrose-H+ uptake by Saccharomyces cerevisiae revealed the presence of two transport systems with high and low affinity for sucrose. The MAL2T permease has a low affinity (K(m) = 120 +/-20 mM) for sucrose, while the alpha-glucoside transporter encoded by the AGT1 gene is a high affinity sucrose-H+ symporter (K(m) = 7.9+/-0.8 mM) that increases the specific growth rate of cells growing on sucrose.

Sugar transport by Saccharomyces cerevisiae protoplasts

Cirillo, Vincent P. (Seton Hall College of Medicine and Dentistry, Jersey City, N.J.). Sugar transport by Saccharomyces cerevisiae protoplasts. J. Bacteriol. 84:1251-1253. 1962.-By the use of Saccharomyces cerevisiae protoplasts, the l-sorbose transport mechanism has been associated with the protoplast membrane rather than the cell wall. The osmotic fragility of protoplasts in l-sorbose solutions shows that the transported sugar remains osmotically active.

Mechanism of glucose transport across the yeast cell membrane

Cirillo, Vincent P. (Seton Hall College of Medicine and Dentistry, Jersey City, N.J.). Mechanism of glucose transport across the yeast cell membrane. J. Bacteriol. 84:485-491. 1962.-The kinetics of d-glucose and l-sorbose transport was studied in Saccharomyces cerevisiae inhibited with iodoacetic acid under nitrogen to prevent glucose metabolism. d-Glucose was found to compete with l-sorbose for a common membrane transport system with an apparent affinity greater than 25 times that of sorbose. A comparison of the net rate of glucose and sorbose transport at 50 and 500 mm external concentration showed that glucose transport is greater than that of sorbose from the lower concentration, but sorbose transport is greater than glucose at the higher concentration. This reversal of transport rate of two sugars with markedly different affinities is predicted by the membrane carrier theory. A further prediction of carrier theory was confirmed by the demonstration that the rate of glucose transport into fructose-loaded cells is greater than into unloaded cells.

CARBOHYDRATE INHIBITORS OF SUCROSE UPTAKE BY RESTING CELLS OF AGROBACTERIUM TUMEFACIENS

The rapid uptake of sucrose-C14from the surrounding medium by resting cells of Agrobacterium tumefaciens is strongly inhibited in a competitive manner by D-glucose, D-galactose, D-xylose, D-fucose, and L-arabinose while their enantiomorphs do not inhibit. It has been possible to formulate specific structural requirements for the monosaccharides which are necessary to produce such powerful inhibitory effects of sucrose uptake.Strong inhibition has also been obtained with 3-ketoglucose, 3-ketosucrose, 3-ketomaltose, 3-ketolactose, and 3-ketotrehalose, as well as with the disaccharides maltose and cellobiose. In these cases, however, specific structural requirements for inhibition have not been determined as yet.

Trehalose metabolism in Saccharomyces cerevisiae during heat-shock

When different strains of Saccharomyces cerevisiae grown at 23 degrees C were transferred to 36 degrees C, trehalose and glycogen were accumulated. Glycogen accumulation was less extensive and its synthesis started at least 15 min after initiation of trehalose synthesis. The steady-state intracellular concentration of trehalose increased simultaneously with the activities of the enzymes trehalose-6P synthase, UDPG-pyrophosphorylase, phosphoglucomutase and trehalase. A small but significant change was observed in hexokinase activity. Our results directly implicate isoform PII of hexokinase and the minor isoform of phosphoglucomutase in the pathway of trehalose formation during heat-shock. We also showed that the major isoform of phosphoglucomutase increased in activity but was not essential for trehalose accumulation. Studies with the glucose uptake system indicated that trehalose accumulation could be primarily determined by intracellular availability of substrates due to the increase in the rate of glucose uptake. The increased uptake appears to have two components: a kinetic effect of temperature upon glucose transporters and an increase in the numbers of molecules of the transporters, probably mediated by synthesis de novo.

Characterization of trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase of Saccharomyces cerevisiae

The properties of yeast trehalose-6-phosphate synthase were reinvestigated in relation with the recent claim made by Panek et al. [Panek, A. C., de Araujo, P. S., Moura-Neto, V. and Panek, A. D. (1987) Curr. Genet. II, 459-465] that the enzyme would be stimulated by ATP and partially inactivated by cAMP-dependent protein kinase. Trehalose-6-phosphate synthase activity was measured by the sum of [14C]trehalose 6-phosphate and [14C]trehalose formed from UDP-[14C]glucose and glucose 6-phosphate. The activity measured in an extract of Saccharomyces cerevisiae was not affected by any treatment of the cells, such as incubation in the presence of glucose or of dinitrophenol, which are known to greatly increase the intracellular concentration of cAMP, nor by preincubation of the extract in the presence of ATP-Mg, cAMP and bovine heart cAMP-dependent protein kinase. The activity was also not significantly different in several mutants affected in the cAMP system. The kinetic properties of the partially purified enzyme were investigated; no effect of ATP could be detected but Pi acted as a potent noncompetitive inhibitor (Ki = 2 mM). The activity of trehalose-6-phosphate phosphatase was measured by the amount of [14C]trehalose formed from [14C]trehalose 6-phosphate. The enzyme could be separated from other phosphatases and appeared to be highly specific for trehalose 6-phosphate. It was Mg dependent and its kinetics for trehalose 6-phosphate was hyperbolic. Studies performed with intact cells, crude extracts or the purified enzyme did not reveal any cAMP-dependent change in its activity. Remarkably, trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase copurified in the course of different chromatographic procedures, suggesting that they are part of a single bifunctional protein. A 50-fold purification of the two enzymes could be achieved with a yield of only 2% by chromatography on Mono S followed by gel filtration on Superose 6B.

Heat-induced accumulation and futile cycling of trehalose in Saccharomyces cerevisiae

Heat shock resulted in rapid accumulation of large amounts of trehalose in Saccharomyces cerevisiae. In cultures growing exponentially on glucose, the trehalose content of the cells increased from 0.01 to 1 g/g of protein within 1 h after the incubation temperature was shifted from 27 to 40 degrees C. When the temperature was readjusted to 27 degrees C, the accumulated trehalose was rapidly degraded. In parallel, the activity of the trehalose-phosphate synthase, the key enzyme of trehalose biosynthesis, increased about sixfold during the heat shock and declined to the normal level after readjustment of the temperature. Surprisingly, the activity of neutral trehalase, the key enzyme of trehalose degradation, also increased about threefold during the heat shock and remained almost constant during recovery of the cells at 27 degrees C. In pulse-labeling experiments with [14C]glucose, trehalose was found to be turned over rapidly in heat-shocked cells, indicating that both anabolic and catabolic enzymes of trehalose metabolism were active in vivo. Possible functions of the heat-induced accumulation of trehalose and its rapid turnover in an apparently futile cycle during heat shock are discussed.

Inactivation of fructose diphosphatase by sucrose in yeast

In Saccharomyces carlsbergensis, the addition of sucrose to the medium led to the inactivation of fructose diphosphatase. Sucrose itself probably triggered this process.

Energy metabolism of Saccharomyces cerevisiae discrepancy between ATP balance and known metabolic functions

The contribution of metabolic pathways to the catabolism of glucose, galactose and ethanol by Saccharomyces cerevisiae in aerobiosis has been studied. The results suggest that: 1. Of the total ATP formed in catabolism yeast obtain as much as 60% from ethylic fermentation during logarithmic growth on glucose. However, about 80% of ATP is formed in oxidation of galactose. Oxidation seems to be the only important catabolic pathway of ethanol. 2. The ratios between growth yield and ATP formed in catabolism were approx. 9, 7 and 3 g dry yeast/mol ATP in glucose, galactose and ethanol cultures, respectively. 3. The balance between ATP produced in catabolism of substrates and the requirements of ATP for the biosynthesis of cellular material indicates that as much as 60% of ATP is spent in functions other than net biosynthesis. 4. The rate of ATP expenditure in non net-biosynthetic functions during growth was approx. 20 mmol/g dry yeast per h. 5. In conditions in which no growth occurred but cell viability was maintained, that is, in the absence of exogenous carbon and nitrogen source, the ATP production rate was approx. 1 mmol ATP/g dry yeast per h. 6. These results indicate that the ATP required for maintaining the yeast alive, what would be considered maintenance energy "sensu stricto", is only a minor proportion of the ATP spent in non net-biosynthetic functions during growth. The identification of the processes related to growth which spend more energy than that required for net biosynthesis could lead to important insights in cell biology.

Genetic co-regulation of galactose and melibiose utilization in Saccharomyces

The gal3 mutation of Saccharomyces, which is associated with an impairment in the utilization of galactose, has been shown to be pleiotropic, causing similar impairments in the utilization of melibiose and maltose. Milibiose utilization and alpha-galactosidase production are directly controlled by the galactose regulatory elements i, c, and GAL4. The fermentation of maltose and the induction of alpha-glucosidase are regulated independently of the i, c, GAL4 system. The production of alpha-galactosidase and galactose-1-phosphate uridyl transferase is coordinate in galactokinaseless strains. Galactose serves as a nonmetabolized, gratuitous inducer of alpha-galactosidase in strains lacking the genes for one or more of the Leloir pathway enzymes.

Reversible permeability changes in the membrane of a yeast cell sugar compartment

Sorbose uptake by Saccharomyces cerevisiae was increased 40 to 60% by glucose and other metabolizable sugars. Neither growth nor binding accounted for the increased uptake. However, accessibility of a restrictive intracellular compartment was increased as shown by counterflow and efflux measurements. Efflux from the compartment was more than doubled by glucose. This effect was reversed by washing and was prevented by iodoacetic acid and other inhibitors, but not by cycloheximide. No evidence was found for a facilitated transport system in the compartment membrane such as exists in the external cell membrane. It was concluded that sorbose crosses the compartment membrane by simple diffusion and that a reaction requiring the metabolism of sugars increases the permeability of the membrane. Arabinose and fucose entered and were lost from the compartment like sorbose, whereas dimethylsulfoxide was unaffected by the compartment. All three of these later compounds were bound by the cells when glucose was available in uptake suspensions. Binding was prevented by iodoacetic acid, but not by cycloheximide.

The absorption of protons with specific amino acids and carbohydrates by yeast

1. Proton uptake in the presence of various amino acids was studied in washed yeast suspensions containing deoxyglucose and antimycin to inhibit energy metabolism. A series of mutant strains of Saccharomyces cerevisiae with defective amino acid permeases was used. The fast absorption of glycine, l-citrulline and l-methionine through the general amino acid permease was associated with the uptake of about 2 extra equivalents of protons per mol of amino acid absorbed, whereas the slower absorption of l-methionine, l-proline and, possibly, l-arginine through their specific permeases was associated with about 1 proton equivalent. l-Canavanine and l-lysine were also absorbed with 1-2 equivalents of protons. 2. A strain of Saccharomyces carlsbergensis behaved similarly with these amino acids. 3. Preparations of the latter yeast grown with maltose subsequently absorbed it with 2-3 equivalents of protons. The accelerated rate of proton uptake increased up to a maximum value with the maltose concentration (K(m)=1.6mm). The uptake of protons was also faster in the presence of alpha-methylglucoside and sucrose, but not in the presence of glucose, galactose or 2-deoxyglucose. All of these compounds except the last could cause acid formation. The uptake of protons induced by maltose, alpha-methylglucoside and sucrose was not observed when the yeast was grown with glucose, although acid was then formed both from sucrose and glucose. 4. A strain of Saccharomyces fragilis that both fermented and formed acid from lactose absorbed extra protons in the presence of lactose. 5. The observations show that protons were co-substrates in the systems transporting the amino acids and certain of the carbohydrates.

Germination and outgrowth of single spores of Saccharomyces cerevisiae viewed by scanning electron and phase-contrast microscopy

Single spores of Saccharomyces cerevisiae were examined during germination and outgrowth by scanning electron and phase-contrast microscopy. Also determined were changes in cell weight and light absorbance, trehalose utilization, and synthesis of protein and KOH-soluble carbohydrates. These studies reveal that development of the vegetative cell from a spore follows a definite sequence of events involving dramatic physical and chemical modifications. These changes are: initial rapid loss in cellular absorbance followed later by an abrupt gain in absorbance; reduction in cell weight and a subsequent progressive increase; modification of the spore surface with concomitant diminution in refractility; elongation of the cell and augmentation of surface irregularities; rapid decline in trehalose content of the cell accompanied by extensive formation of KOH-soluble carbohydrates; and bud formation.

Carbohydrate accumulation during the sporulation of yeast

The sporulation of Saccharomyces cerevisiae is characterized by an increase in dry weight without cell division. At least 67% of the dry weight increase is due to the synthesis of cellular carbohydrates consisting of trehalose and insoluble components. The insoluble carbohydrates accumulate only during the period preceding the actual formation of visible ascospores. The trehalose accumulates throughout the sporulation cycle and is specifically localized in the ascospore.

Intracellular trehalase of a hybrid yeast

1. The trehalase found in an extract prepared from a yeast strain that cannot ferment trehalose was studied and characterized. The enzyme is highly specific for trehalose with K(m) 1.02x10(-2)m, and an optimum pH of 6.9. 2. It is inhibited by glucose and by trehalose 6-phosphate, and does not facilitate any significant transglucosylations. 3. pK values 7.7 and 5.8 were detected for the groups associated with binding of the non-ionized substrate to the enzyme. 4. The trehalase was found to be highly labile and was inhibited by thiol-binding reagents. 5. The possible role of this enzyme in the trehalose-dissimilation patterns in the yeast cell was evaluated.

On the active transport of sucrose and of 3-keto-sucrose in Agrobacterium tumefaciens

The active transport of sucrose and of 3-ketosucrose into resting cells of Agrobacterium tumefaciens was established. Evidence is presented to show that these two transport systems behave differently. Their dependence on temperature, the effects of inhibitors, and the effects of stationary incubation vs. agitation are among the parameters studied. Inorganic ions had no effect on the active transport of sucrose-C14. Estimates of the degree of intracellular accumulation of sucrose-C14were made.