Uptake of amino acids by actidione-treated yeast cells. I. Specificity of carriers

Effects of the Fenton reagent on transport in yeast

In the facultatively anaerobic yeast Saccharomyces cerevisiae the uptake rate and the accumulation ratio of 2-aminoisobutyric acid was decreased by some 30% by Fenton's reagent (FR), a powerful source of OH. radicals. Likewise, the uptake of glutamic acid, leucine and arginine was diminished. The mediated diffusion of 6-deoxy-D-glucose was not affected. The H+ symport of maltose and trehalose was inhibited by some 40% both in the initial rate and in the accumulation ratio. FR had a dramatic inhibitory effect when present during preincubation with 50 mmol/L glucose. In the obligately aerobic Lodderomyces elongisporus the uptake of all amino acids tested was decreased by 15-30%, that of 6-deoxy-D-glucose by about 10%. The initial rates of uptake of maltose and trehalose were depressed by FR by 40% and the acceleration of uptake observed after 8 min of incubation, was abolished by FR completely. Acidification rate of the external medium by S. cerevisiae in the presence of glucose or galactose was enhanced three-fold, that after subsequently added K+ was substantially decreased. FR appears to have a dual effect on sugar and amino acid transport processes in yeast: (1) it blocks carrier protein synthesis; (2) it inhibits the source of energy for transport. It does not appreciably affect the carrier proteins themselves.

Uptake of L-lysine by a double mutant of Saccharomyces cerevisiae

A gap1 can1 mutant of Saccharomyces cerevisiae with a single lysine transport system remaining was used to study detailed kinetics of this transport. Its half-saturation constant was 78 mumol per litre, its maximum rate of transport was 0.29 mumol L-lysine per g dry matter per minute, both parameters being lower by more than an order of magnitude in comparison with the GAP system. The pH optimum lay at very acid values of about 3, the temperature dependence without any transition point showed an activation energy of 48 kJ/mol. The transport was inhibited by common metabolic inhibitors (3'-chlorophenylhydrazonomalononitrile, antimycin, 2-deoxy-D-glucose, sodium arsenate) as well as by a membrane-active one (uranyl nitrate). The specificity of the system was extremely high, none of the natural amino acids acting as competitor to L-lysine. The maximum accumulation ratio attained (at about 5 mg dry matter per mL) was 100: 1-120: 1, in agreement with the measured protonmotive force under the assumption of 1 H+ ion being transported with 1 lysine molecule. The ratio decreased with increasing external concentration of lysine to as little as 4: 1 at 1 mmol lysine per litre. It also decreased with increasing suspension density and it was at extremely low suspension densities (0.2 mg dry matter per mL) that ratios of as much as 500: 1 were reached. Application of group-specific inhibitors showed that the active site of the carrier contains an essential histidine residue.

Inhibition of growth and uptake of amino acids in the yeast, Candida parapsilosis, by ambruticin

The antifungal antibiotic, ambruticin, inhibits growth of Candida parapsilosis and reduces its ability to take up amino acids. Increasing growth temperature from 30 degrees C to 39 degrees C leads to a 100-fold decrease in the minimum growth inhibitory concentration. Ambruticin is 20 times more effective at pH 5 than at pH 8 and exponentially growing cultures are much less susceptible than stationary phase cells. The activity of ambruticin is also dependent on the presence of certain exogenous nutrients. When acetate or succinate (10 mM) are included in the incubation medium, ambruticin has little effect on amino acid uptake. Glucose, mannose and glycerol do not decrease the efficacy of ambruticin. Ambruticin probably inhibits growth by reducing the utilization of exogenous and intracellular carbohydrates. This leads to a fall in energy production within the cell which can be monitored as a reduction in the activity of energy-dependent transport systems.

Anilinonaphthalene sulfonate fluorescence and amino acid transport in yeast

Fluorescence of 1-anilinonaphthalene-8-sulfonate in yeast membranes appears to be caused predominantly by binding to lipids (ANS protein:ANS lipid approximately 1 : 20) as indicated by the fluorescence lifetime, degree of polarization, and excitation spectra. It was insensitive to short-circuiting the membrane potential. Fluorescence intensity increased as cells (especially after pretreatment with energy donors such as glucose) were exposed to some amono acids, in particular, aspartic and glutamic acids. The character of fluorescence shifted to that of protein-bound ANS, suggesting an exposure of new protein sites accessible to the probe. This shift could be prevented by inhibitors of energy transduction as well as of transport. The K1/2 of the shift was at 2.5 mM aspartic acid.

L-Proline transport in Saccharomyces cerevisiae

Transport of L-proline into Saccharomyces cerevisiae K is mediated by two systems, one with a KT of 31 microM and Jmax of 40 nmol . s-1 . (g dry wt.)-1, the other with KT greater than 2.5 mM and Jmax of 150-165 nmol . s-1 . (g dry wt.)-1. The kinetic properties of the high-affinity system were studied in detail. It proved to be highly specific, the only potent competitive inhibitors being (i) L-proline and its analogs L-azetidine-2-carboxylic acid, sarcosine, D-proline and 3,4-dehydro-DL-proline, and (ii) L-alanine. The other amino acids tested behaved as noncompetitive inhibitors. The high-affinity system is active, has a sharp pH optimum at 5.8-5.9 and, in an Arrhenius plot, exhibits two inflection points at 15 degrees C and 20-21 degrees C. It is trans-inhibited by most amino acids (but probably only the natural substrates act in a trans-noncompetitive manner) and its activity depends to a considerable extent on growth conditions. In cells grown in a rich medium with yeast extract maximum activity is attained during the stationary phase, on a poor medium it is maximal during the early exponential phase. Some 50-60% of accumulated L-proline can leave cells in 90 min (and more if washing is done repeatedly), the efflux being insensitive to 0.5 mM 2,4-dinitrophenol and uranyl ions, the pH between 3 and 7.3, as well as to the presence of 10-100 mM unlabeled L-proline in the outside medium. Its rate and extent are increased by 1% D-glucose and by 10 micrograms nystatin per ml.

Stimulation of amino acid transport in Saccharomyces cerevisiae by metabolic inhibitors

Inhibitors of energy metabolism (3-chlorophenylhydrazonomalononitrile, antimycin A, iodoacetamide, dicyclohexylcarbodiimide) but not of transport (uranyl ions) stimulate at low concentrations the uptake of L-leucine, L-glutamic acid, L-arginine and, to a lesser degree, of 2-aminoisobutyric acid in Saccharomyces cerevisiae. The effect is apparent only after augmenting the energy reserves of cells by preincubation with D-glucose or, more strikingly, with ethanol. It is absent in a mutant (op1) lacking the translocation system for ADP--ATP in mitochondria. The presence of two different energy reserves for amino acid transport is indicated (one in energy-poor, the other in energy-rich cells). The stimulating effect appears to be caused by a retarded degradation of the transport proteins as occurs at a lowered level of mitochondria-produced ATP.

Transport of ribitol and D-glucose in the yeast Candida guillermondii

The uptakes of the linear polyol ribitol and of D-glucose by Candida guillermondii were found to be carrier-mediated and to require metabolic energy. In glucose-grown cells ribitol possibly enters by simple diffusion but after an induction period a specific transport system is synthesized, inhibitable by higher concentrations of arabinitols, xylitol, mannitol and sorbitol. Actidione blocks the synthesis of the inducible ribitol transport system. Two systems of different affinity for substrate were found to operate in the uptake of both glucose and of ribitol. Counter-transport experiments with ribitol, D-glucose and 3-O-methyl-D-glucose support the carrier nature of the uptake system.

Manganese mutagenesis in yeast. VI. Mn2+ uptake, mitDNA replication and ER induction: comparison with other divalent cations

A medium was found in which manganese efficiently induces erythromycin-resistant mitochondrial mutations, and which is suitable for measuring Mn2+ uptake and the labelling of DNA (fig. 1). Mn2+ uptake is stimulated by glucose and slowed down by cycloheximide (Fig 2). Mg2+ competes with Mn2+ uptake much stronger than does Zn2+ (Fig. 3). All of the conditions which favour Mn2+ uptake also favour induction of erythromycin-resistant mutations (Tables 3, 4). Mn2+ strongly inhibits protein synthesis (Table 1). Nuclear DNA replication is also strongly inhibited by this cation, while mitochondrial DNA replication is only weakly inhibited during the first 3 h of labelling, but there is small if any increase of the label incorporation between the 3rd 6th h of labelling (Table 2). The relation between label incorporation into mitDNA and mutation induction by manganese is not straightforward (Table 5). From among 11 divalent cations tested, only Mn2+ was capable of inducing mitochondrial erythromycin-resistant mutations (Table 6).

Uptake and incorporation of pyrimidines in Euglena gracilis

In photoorganotrophically grown cells of Euglena gracilis the uptake and incorporation degree of 12 different pyrimidines were tested. The rate of uptake of pyrimidines has distinct maxima in the late log phase and in the stationary phase of cell multiplication. The kinetics of uptake are linear in the first 2 h, do not show saturation at various concentrations and increase with the concetrations. No accumulation of the pyrimidines at various concentrations could be observed in the first 2 h of incubation. Membrane inhibitors as uranyl acetate inhibit the uptake of the reference substance alpha-AIB, which is wellknown transported by an active transport mechanism, but have no effect on uptake rate of uracil and cytosine. It could not be observed an energy requirement tested in temperature dependence and with electron transport inhibitors. Uptake of uridine, uracil, barbituric acid and alpha-AIB is inhibited by cycloheximide in a different manner after 5 - 10 min.

The concentration of glycine by preparations of the yeast Saccharomyces Carlsbergensis depleted of adenosine triphosphate: Effects of proton gradients and uncoupling agents

1. At pH 4.5 and 30degreesC, yeast preparations depleted of ATP in the presence of antimycin and deoxyglucose spontaneously lost K+, gaining roughly an equivalent amount of H+. 2. Five proton conductors including azide and 2,4-dinitrophenol accelerated this process, as did [14C]glycine, which was absorbed with two extra equivalents of H+. 3. The rate of glycine uptake at pH 4.5 diminished fourfold when cellular K+ fell by 20%. 4. The distribution of [14C]propionate indicated that the intracellular pH fell from 6.2 to 5.7 when the cellular content of K+ fell by 30%. 5. Glycine uptake from a 5 muM solution was about 400 times faster at pH 4.5 than it was at pH 7.4 with 100mM-KC1 present ostensibly to lower the membrane potential. 6. Yeast preparations containing 2mM-[14C]glycine absorbed a further amount from a 0.1 muM solution at pH 4.5. After about 10 min a net movement of [14C]glycine out of the yeast occurred. The ratio of the cellular [14Ia1glycine concentration to the concentration outside the yeast reached 4 X 10(4) in these assays, whereas at pH 7.4 in the presence of 100mM-KC1 it did not exceed 15 in 3h. Dimitrophenol lowered the accumulation ratio at pH 4.5, apparently by causing proton conduction. 7. The observations are consistent with the notion that glycine uptake is driven by a proton symport mechanism. 8. Possible factors governing the strikingly low rate of glycine efflux as opposed to its optimum rate of influx are discussed.

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-dgcl) were prepared by catalytic hydrogenolysis of the corresponding deoxyiodo derivatives with gaseous tritium. The two sugars are transported into Saccharomyces 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 degrees 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.

Characterization of a specific transport system for arginine in isolated yeast vacuoles

The transport of L-arginine was studied in isolated vacuoles of Saccharomyces cerevisiae. A centrifugation method allowed rapid separation of the fragile vacuoles from the incubation media so that initial uptake rates of [14C]arginine could be measured. Labelled arginine added to the medium was accumulated in the isolated vacuoles; it was found to exchange specifically with the arginine already present in the vacuoles. Such an exchange did not take place in intact spheroplasts. The pH dependence of the arginine transport in the vacuoles was tested. As the vacuoles are unstable in the pH range of optimal transport activity (pH above 7.0), the pH optimum of the transport reaction could not be determined. From the temperature dependence, the apparent energy of activation was calculated to be 9800 cal/mol. Arginine transport shows saturation kinetics with an apparent Km of 30 muM in the isolated vacuoles, and of 1.5 muM in the spheroplasts. Competition experiments with amino acids and arginine analogues demonstrated that the arginine transport in both vacuoles and spheroplasts, is highly specific. The two systems, however, were shown to have distinct specificities. The inhibition of vacuolar L-arginine transport by D-arginine, L-histidine, and L-canavanine was competitive with apparent Ki values of 60 muM, 400 muM and 600 muM respectively.

Properties of alpha-aminoisobutyric acid transport in a thermophilic microorganism

Uptake of alpha-aminoisobutyric acid (AIB) by a leucine-tyrosine auxotroph of a thermophilic microorganism starved for leucine was studied. AIB was taken up by the cells against a substantial concentration gradient (300:1) and was present there in a free and unchanged form. Various energy inhibitors and sulfhydryl reagents strongly inhibited the accumulation of AIB. AIB uptake obeyed saturation kinetics, and the Lineweaver-Burk plot is characterized by a biphasic curve. AIB most probably shares a common transport system(s) with alanine, serine, and glycine. A mutant defective in l-alanine uptake was isolated by using the suicide effect due to accumulation of the tritiated substrate. The mutant also exhibited impaired transport activity towards AIB, glycine, and l-serine, but not to phenylalanine or valine. The transport of AIB, glycine, l-alanine, and l-serine was induced by d-alanine (5 x 10(-3) M) during growth in a succinate- and ammonia-containing medium. De novo protein synthesis was required for the induction of AIB transport; the induction was inhibited when growth occurred in glucose-containing media. The apparent differential rate of synthesis of the AIB transport system was decreased considerably in glucose-grown cells as compared to succinate-grown cells. A common genetic basis of either the regulatory or structural nature for the transport of AIB, alanine, glycine, and serine in a thermophilic microorganism is suggested.