Uptake Of Aspartic Acid Research Articles

Effect of ACGT motif in spatiotemporal regulation of AtAVT6D, which improves tolerance to osmotic stress and nitrogen-starvation.

Plasma membrane-localized AtAVT6D importing aspartic acid can be targeted to develop plants with enhanced osmotic and nitrogen-starvation tolerance. AtAVT6D promoter can be exploited as a stress-inducible promoter for genetic improvements to raise stress-resilient crops. The AtAVT6 family of amino acid transporters in Arabidopsis thaliana has been predicted to export amino acids like aspartate and glutamate. However, the functional characterization of these amino acid transporters in plants remains unexplored. The present study investigates the expression patterns of AtAVT6 genes in different tissues and under various abiotic stress conditions using quantitative Real-time PCR. The expression analysis demonstrated that the member AtAVT6D was significantly induced in response to phytohormone ABA and stresses like osmotic and drought. The tissue-specific expression analysis showed that AtAVT6D was strongly expressed in the siliques. Taking together these results, we can speculate that AtAVT6D might play a vital role in silique development and abiotic stress tolerance. Further, subcellular localization study showed AtAVT6D was localized to the plasma membrane. The heterologous expression of AtAVT6D in yeast cells conferred significant tolerance to nitrogen-deficient and osmotic stress conditions. The Xenopus oocyte studies revealed that AtAVT6D is involved in the uptake of Aspartic acid. While overexpression of AtAVT6D resulted in smaller siliques in Arabidopsis thaliana. Additionally, transient expression studies were performed with the full-length AtAVT6D promoter and its deletion constructs to study the effect of ACGT-N24-ACGT motifs on the reporter gene expression in response to abiotic stresses and ABA treatment. The fluorometric GUS analyses revealed that the promoter deletion construct-2 (Pro.C2) possessing a single copy of ACGT-N24-ACGT motif directed the strongest GUS expression under all the abiotic conditions tested. These results suggest that Pro.C2 can be used as a stress-inducible promoter to drive a significant transgene expression.

Hygroscopicity of amino acids and their effect on the water uptake of ammonium sulfate in the mixed aerosol particles

Amino acids are important water-soluble nitrogen-containing compounds in atmospheric aerosols. They can be involved in cloud formation due to their hygroscopicity and have significant influences on the hygroscopicity of inorganic compounds, which have not yet been well characterized. In this work, the hygroscopic properties of three amino acids, including aspartic acid, glutamine, and serine, as well as their mixtures with ammonium sulfate (AS) were investigated using a hygroscopicity tandem differential mobility analyzer (HTDMA) system. The gradual water uptake of aspartic acid, glutamine and serine particles indicates that they exist as liquid phase at low RH. When mixing either aspartic acid or glutamine with AS by mass ratio of 1:3, we observed a clear phase transition but with a lower deliquescence relative humidity (DRH) with respect to that of pure AS. This suggests the crystallization of AS in the presence of each of these two amino acids. However, as the mass fractions of these two amino acids increased in the mixed particles, the deliquescence transition process was not obvious. In contrast, the crystallization of AS was efficiently hampered even at low content (i.e., 25% by mass) of serine in the mixed particles. The Zdanovskii-Stokes-Robinson (ZSR) method in general underestimated the hygroscopic growth of any mixtures at RH below 79% (prior to AS deliquescence), suggesting both amino acid and the partially dissolved AS contributed the overall hygroscopicity at RH in this range. Relatively good agreements were reached between the measurements and model predictions using the Extended Aerosol Inorganic Model (E-AIM) assuming solid state AS in the mixed particles for 1:3 aspartic acid-AS and glutamine-AS systems. However, the model failed to simulate the water uptake behaviors of any other systems. It demonstrates that the interactions between components within the aerosols have a significant effect on the phase state of the mixed particles.

Amyloid-beta peptide decreases expression and function of glutamate transporters in nervous system cells

Glutamate is an essential excitatory neurotransmitter that regulates brain functions, and its activity is tightly regulated by glutamate transporters. Excess glutamate in the synaptic cleft and dysfunction of excitatory amino acid transporters have been shown to be involved in development of Alzheimer’s disease, but the precise regulatory mechanism is poorly understood. Using a D-[3H]-aspartic acid uptake assay, we found that Aβ1-42 oligomers impaired glutamate uptake in astrocytes and neurons. In astrocytes, this process was accompanied by reduced expression of GLT-1 and GLAST as detected by Western blot and immunocytofluorescence. However, mRNA levels of EAATs detected by qPCR in astrocytes and neurons were not altered, which suggests that this process is post-translational. Co-localization analysis using immunocytofluorescence showed that ubiquitylation of GLT-1 significantly increased. Therefore, we hypothesized that Aβ1-42 oligomers-induced endocytosis of astrocytic GLT-1 may be involved in ubiquitylation. In addition, Aβ1-42 oligomers enhanced secretion of IL-1β, TNF-α, and IL-6 into culture supernatant, which may be correlated with an inflammatory response and altered EAATs expression or function in Alzheimer’s disease. These findings support the idea that dysregulation of the glutamatergic system may play a significant role in pathogenesis of Alzheimer’s disease. Furthermore, enhancing expression or function of EAATs in astrocytes and neurons might be a new therapeutic approach in treatment of Alzheimer’s disease.

Amino acid uptake in arbuscular mycorrhizal plants.

We examined the extent to which arbuscular mycorrhizal (AM) fungi root improved the acquisition of simple organic nitrogen (ON) compounds by their host plants. In a greenhouse-based study, we used quantum dots (fluorescent nanoparticles) to assess uptake of each of the 20 proteinaceous amino acids by AM-colonized versus uncolonized plants. We found that AM colonization increased uptake of phenylalanine, lysine, asparagine, arginine, histidine, methionine, tryptophan, and cysteine; and reduced uptake of aspartic acid. Arbuscular mycorrhizal colonization had the greatest effect on uptake of amino acids that are relatively rare in proteins. In addition, AM fungi facilitated uptake of neutral and positively-charged amino acids more than negatively-charged amino acids. Overall, the AM fungi used in this study appeared to improve access by plants to a number of amino acids, but not necessarily those that are common or negatively-charged.

Transport of aspartic acid, arginine, and tyrosine by the opportunistic protist Pneumocystis carinii

In order to improve culture media and to discover potential drug targets, uptake of an acidic, a basic, and an aromatic amino acid were investigated. Current culture systems, axenic or co-cultivation with mammalian cells, do not provide either the quantity or quality of cells needed for biochemical studies of this organism. Insight into nutrient acquisition can be expected to lead to improved culture media and improved culture growth. Aspartic acid uptake was directly related to substrate concentration, Q 10 was 1.10 at pH 7.4. Hence the organism acquired this acidic amino acid by simple diffusion. Uptake of the basic amino acid arginine and the aromatic amino acid tyrosine exhibited saturation kinetics consistent with carrier-mediated mechanisms. Kinetic parameters indicated two carriers ( K m=22.8±2.5 μM and K m=3.6±0.3 mM) for arginine and a single carrier for tyrosine ( K m=284±23 μM). The effects of other L-amino acids showed that the tyrosine carrier was distinct from the arginine carriers. Tyrosine and arginine transport were independent of sodium and potassium ions, and did not appear to require energy from ATP or a proton motive force. Thus facilitated diffusion was identified as the mechanism of uptake. After 30 min of incubation, these amino acids were incorporated into total lipids and the sedimentable material following lipid extraction; more than 90% was in the cellular soluble fraction.

A new structural class of subtype-selective inhibitor of cloned excitatory amino acid transporter, EAAT2

We have studied the pharmacological effects of ( RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) and the enantiomers of ( RS)-2-amino-3-(3-hydroxy-1,2,5-thiadiazol-4-yl)propionic acid (TDPA) on cloned human excitatory amino acid transporter subtypes 1, 2 and 3 (EAAT1–3) expressed in Cos-7 cells. Whereas AMPA and ( R)-TDPA were both inactive as inhibitors of [ 3H]-( R)-aspartic acid uptake on all three EAAT subtypes, ( S)-TDPA was shown to selectively inhibit uptake by EAAT2 with a potency equal to that of the endogenous ligand ( S)-glutamic acid. ( S)-TDPA thus represents a new structural class of EAAT2 inhibitor that will serve as a lead for the design of EAAT selective inhibitors.

Blood-brain barrier produces significant efflux of L-aspartic acid but not D-aspartic acid: in vivo evidence using the brain efflux index method.

The brain efflux index method has been used to clarify the mechanism of efflux transport of acidic amino acids such as L-aspartic acid (L-Asp), L-glutamic acid (L-Glu), and D-aspartic acid (D-Asp) across the blood-brain barrier (BBB). About 85% of L-[3H]Asp and 40% of L-[3H]Glu was eliminated from the ipsilateral cerebrum within, respectively, 10 and 20 min of microinjection into the brain. The efflux rate constant of L-[3H]Asp and L-[3H]Glu was 0.207 and 0.0346 min(-1), respectively. However, D-[3H]Asp was not eliminated from brain over a 20-min period. The efflux of L-[3H]Asp and L-[3H]Glu was inhibited in the presence of excess unlabeled L-Asp and L-Glu, whereas D-Asp did not inhibit either form of efflux transport. Aspartic acid efflux across the BBB appears to be stereospecific. Using a combination of TLC and the bioimaging analysis, attempts were made to detect the metabolites of L-[3H]Asp and L-[3H]Glu in the ipsilateral cerebrum and jugular vein plasma following a microinjection into parietal cortex, area 2. Significant amounts of intact L-[3H]Asp and L-[3H]Glu were found in all samples examined, including jugular vein plasma, providing direct evidence that at least a part of the L-Asp and L-Glu in the brain interstitial fluid is transported across the BBB in the intact form. To compare the transport of acidic amino acids using brain parenchymal cells, brain slice uptake studies were performed. Although the slice-to-medium ratio of D-[3H]Asp was the highest, followed by L-[3H]Glu and L-[3H]Asp, the initial uptake rate did not differ for both L-[3H]Asp and D-[3H]Asp, suggesting that the uptake of aspartic acid in brain parenchymal cells is not stereospecific. These results provide evidence that the BBB may act as an efflux pump for L-Asp and L-Glu to reduce the brain interstitial fluid concentration and act as a static wall for D-Asp.

Organic matrix synthesis in the scleractinian coral stylophora pistillata: role in biomineralization and potential target of the organotin tributyltin

The kinetics of organic matrix biosynthesis and incorporation into scleractinian coral skeleton was studied using microcolonies of Stylophora pistillata. [14C]Aspartic acid was used to label the organic matrix since this acidic amino acid can represent up to 50 mol % of organic matrix proteins. External aspartate was rapidly incorporated into tissue protein without any detectable lag phase, suggesting either a small intracellular pool of aspartic acid or a pool with a fast turn-over rate. The incorporation of 14C-labelled macromolecules into the skeleton was linear over time, after an initial delay of 20 min. Rates of calcification, measured by the incorporation of 45Ca into the skeleton, and of organic matrix biosynthesis and incorporation into the skeleton were constant. Inhibition of calcification by the Ca2+ channel inhibitor verapamil reduced the incorporation of organic matrix proteins into the skeleton. Similarly, organic matrix incorporation into the skeleton, but not protein synthesis for incorporation into the tissue compartment, was dependent on the state of polymerization of both actin and tubulin, as shown by the sensitivity of this process to cytochalasin B and colchicin. These drugs may inhibit exocytosis of organic matrix proteins into the subcalicoblastic space. Finally, inhibition of protein synthesis by emetin or cycloheximide and inhibition of N-glycosylation by tunicamycin reduced both the incorporation of macromolecules into the skeleton and the rate of calcification. This suggests that organic matrix biosynthesis and its migration towards the site of calcification may be a prerequisite step in the calcification process. On the basis of these results, we investigated the effects of tributyltin (TBT), a component of antifouling painting known to interfere with biomineralization processes. Our results have shown that this xenobiotic significantly inhibits protein synthesis and the subsequent incorporation of protein into coral skeleton. This effect was correlated with a reduction in the rate of calcification. Protein synthesis was shown to be the parameter most sensitive to TBT (IC50=0.2 micromol l-1), followed by aspartic acid uptake by coral tissue (IC50=0.6 micromol l-1), skeletogenesis (IC50=3 micromol l-1) and Ca2+ uptake by coral tissue (IC50=20 micromol l-1). These results suggest that the mode of action of TBT on calcification may be the inhibition of organic matrix biosynthesis.

Regulation of taurine transport in human colon carcinoma cell lines (HT-29 and Caco-2) by protein kinase C

The effect of phorbol 12-myristate 13-acetate (PMA), a phorbol ester known to stimulate protein kinase C, on taurine transport was studied in the human colon carcinoma cell line HT-29. PMA (1 microM) was found to inhibit taurine uptake in confluent monolayers of this cell line by approximately 70% after pretreatment of the cells with the compound for 1 h (IC50 = 42.7 +/- 2.6 nM). The inhibitory effect of PMA on the taurine transporter could be confirmed by using beta-alanine, another substrate for the transporter. Kinetic analysis of taurine uptake indicated that the PMA effect was associated with a decrease in the maximal velocity (954 +/- 26 vs. 676 +/- 28 pmol.10 min-1.mg of protein-1) and an increase in the Michaelis-Menten constant (9.8 +/- 0.5 vs. 13.3 +/- 1.0 microM). The inhibition of taurine uptake could be blocked by cotreatment of the cultures with staurosporine, an inhibitor of protein kinase C. The inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate had no effect. Treatment of the cells with PMA did not alter the uptake of leucine and lysine, stimulated the uptake of aspartic acid, and inhibited the uptake of proline. The PMA effect on taurine uptake was not prevented by cycloheximide, actinomycin D, colchicine, or cytochalasin D. Comparison of the taurine transport activity in HT-29 cells with that in Caco-2, another human colon carcinoma cell line, revealed that the latter cell line also expressed the taurine transporter but at a much reduced level (about one-fifth compared with HT-29).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential inhibition by Bacillus thuringiensis δ endotoxin of leucine and aspartic acid uptake into BBMV from midgut of Manduca sexta

Pre-incubation of brush border membrane vesicles (BBMV) isolated from the midgut of Manduca sexta with activated Bacillus thuringiensis δ edotoxin for a short period resulted in differential inhibition of K +-dependent transport of leucine relative to the effect on K +-dependent transport of aspartic acid. The difference in I 1 2 (5 fold greater for aspartic acid than for leucine) is interpreted as the result of enhanced binding of the B. thuringiensis δ endotoxin to the leucine transport system.

Transport of Arginine and Aspartic Acid into Isolated Barley Mesophyll Vacuoles

The transport of arginine into isolated barley (Hordeum vulgare L.) mesophyll vacuoles was investigated. In the absence of ATP, arginine uptake was saturable with a K(m) of 0.3 to 0.4 millimolar. Positively charged amino acids inhibited arginine uptake, lysine being most potent with a K(i) of 1.2 millimolar. In the presence of free ATP, but not of its Mg-complex, uptake of arginine was drastically enhanced and a linear function of its concentration up to 16 millimolar. The nonhydrolyzable adenylyl imidodiphosphate, but no other nucleotide tested, could substitute for ATP. Therefore, it is suggested that this process does not require energy and does not involve the tonoplast ATPase. The ATP-dependent arginine uptake was strongly inhibited by p-chloromercuriphenylsulfonic acid. Furthermore, hydrophobic amino acids were inhibitory (I(50) phenylalanine 1 millimolar). Similar characteristics were observed for the uptake of aspartic acid. However, rates of ATP-stimulated aspartic acid transport were 10-fold lower as compared to arginine transport. Uptake of aspartate in the absence of ATP was negligible.

Changes in medium radioactivity and composition accompany high-affinity uptake of glutamate and aspartate by mouse brain slices.

In measurements of high affinity transport in tissue slices, the incubation medium is often treated as an "infinitely large pool". External substrate concentrations, even at the micromolar level, are assumed to be constant and metabolic interactions between tissue and medium are neglected. In the present report we describe experiments in which glutamic and aspartic acid uptake by mouse brain slices were studied using techniques that could test these assumptions. Cerebral hemispheres were cut into 0.1 mm sections and about 90 mg of tissue incubated in 10 ml of oxygenated medium. After 45 minutes of equilibration, radioactive substrates were added and the concentrations and specific activities of the amino acids and their metabolites in the medium were determined. During the first 10 min following substrate addition, rapid decreases in glutamic and aspartic acid concentrations in the medium were accompanied by large decreases in specific activity caused by the continuous release of these amino acids from the tissue. In addition, extensive conversion of both substrates to glutamine and the preferential accumulation of this metabolite, in the medium, was found. These results demonstrate that metabolism and release occur simultaneously with uptake during transport experiments in vitro and that these processes can take place in specific tissue compartments. It is therefore necessary to measure the tissue and medium concentration levels of amino acids along with their radioactivity in such experiments, since all three processes (transport, metabolism, and compartmentation) are interrelated in the clearance of amino acids from the incubation medium and probably from the extracellular spaces in vivo as well.

The effect of delta-aminolaevulinic acid on the high affinity uptake of aspartic acid by rat brain synaptosomes

1. 1. δ-Aminolaevulinic (δ-ALA) acid is an analogue of GABA, glutamate and asparate. 2. 2. High affinity GABA uptake by synaptosomes is inhibited by δ-ALA in a competitive fashion at high concentrations (> 0.5 mM). 3. 3. Glutamate uptake is inhibited in a non-competitive fashion at all δ-ALA concentrations (0.05-2.0 mM). 4. 4. High affinity aspartate uptake is inhibited in a non-competitive fashion at high concentration (> 1.0 mM) but exhibits a curve which resembles that for the inhibition of GABA uptake. 5. 5. The different interactions between δ-ALA, glutamate and aspartate may be evidence for a separate transport system for aspartate.

The aerobic mineralization of organic compounds in the saline Lake Grevelingen (The Netherlands) (VI)

During a one year period the uptake of aspartic acid and of a mixture of amino acids was determined using14C-labeled substrates as described by WRIGHT and HOBBIE (1966). By this technique the activity is analyzed of that part of the bacterial population which is able to utilize the added substrate. For comparison purposes the activity of the total heterotrophic bacterial population was determined by measurement of the oxygen consumption rate. From the oxygen consumption rate (mg O2.l−1.h−1) the carbon mineralization rate (mg C.l−1.h−1) was calculated by applying a conversion factor of 0.29.

Dicarboxylic amino acid uptake in normal, Friedreich's ataxia, and dicarboxylic aminoaciduria fibroblasts.

Glutamic and aspartic acid uptake was measured in skin fibroblasts from patients with Friedreich's Ataxia, dicarboxylic aminoaciduria, and normal individuals. The results showed no difference in uptake kinetics of either dicarboxylic amino acids between Friedreich's Ataxia and normal cells, but reduced uptake velocities in dicarboxylic aminoaciduria fibroblasts. Friedreich's Ataxia fibroblasts were, however, less calcium-dependent and more magnesium and phosphate-dependent than controls in glucose-free incubation mixture. This difference might be related to some degree of glucose intolerance by Friedreich's Ataxia fibroblasts in culture.

Interactions of amino acids with hydrous metal oxides: I. Chromium hydroxide- d-aspartic acid system

The sorption of aspartic acid on a monodispersed chromium hydroxide sol consisting of uniform spherical particles was studied as a function of pH, temperature, and the amino acid concentration. The uptake of aspartic acid is strongly dependent on pH and shows maximum sorption at pH ∼ 5–6. The amounts adsorbed increase with increasing concentration of the amino acid and no saturation could be achieved. Furthermore, considerably larger amounts were sorbed at 90 than at 25°C. These results indicate that aspartic acid is absorbed in the particles, most likely as a consequence of chelation to chromium ions. No adsorption of tryptophan could be detected on the same colloidal particles. The difference in the behavior of aspartic acid and tryptophan is discussed.

KINETICS OF AMINO ACID INFLUX INTO NITELLA FLEXILIS1

SUMMARYThe uptake of amino acids by Nitella flexilis has been investigated. Influx of glycine, alanine, and valine appears to be a diffusive process. Influx ranged from 0.14 to 0.06 and 0.04 pmoles/(cm)(sec), respectively. Aspartic acid uptake is an active transport mechanism. The Vmax is 2.8 pmoles/(cm)(sec); the transport constant (Michaelis constant) Km, 7.8 × 10−3 M. The uptake of arginine is apparently due to 2 transport systems, one with a Vmax and Km of 3.1 pmoles/(cm)(sec) and 3.2 × 10−3M, respectively. The second system has a Vmax of 1.4 pmoles/(cm)(sec) and a Km of 2.1 × 10−4 M. The possibility that the second system is diffusive has been considered.

Comparative transport activity of intact cells, membrane vesicles, and mesosomes of Bacillus licheniformis.

Sodium ion was shown to stimulate strongly the transport of l-glutamic acid into cells of Bacillus licheniformis 6346 His(-). Lithium ion had a slight capacity to replace Na(+) in this capacity, but K(+) was without effect. Three of five amino acids tested. l-glutamic acid, l-aspartic acid, and l-alanine, were concentrated against a gradient in the cells. Intracellular pools of these amino acids were extractable with 5% trichloroacetic acid. Pools of l-histidine and l-lysine could not be detected. No evidence of active transport of lysine into cells could be detected, and histidine was taken up in the absence of chloramphenicol but not in its presence. The uptake of glutamic acid by membrane vesicle preparations was strongly stimulated by reduced nicotinamide adenine dinucleotide (NADH) and to a lesser extent by succinate. The presence of phenazine methosulfate increased uptake in the presence of succinate. Either l- or d-lactate and adenosine triphosphate were without effect. None of these compounds stimulated the uptake of glutamic acid by mesosomes, although some mesosome preparations contained separable membrane which was very active. NADH strongly stimulated the uptake of aspartic acid and alanine by membrane vesicles but had only a slight effect on the uptake of histidine and lysine. No evidence of active transport of any of the amino acids into mesosomes could be detected either in the presence or absence of NADH. NADH stimulation of the uptake of glutamic acid by membrane vesicles was destroyed by exposure to light of 360 nm; this inactivation was reversible by vitamin K(2(5)) or K(2(10)). Sodium ion stimulated transport of glutamic acid by membrane vesicles.

Utilization of oxygen, glucose, and carbon dioxide by Echinorhynchus gadi

Specimens of the acanthocephalan, Echinorhynchus gadi, were taken from the gut of the winter flounder, Pseudopleuronectes americanus, caught by commercial fishermen off Point Judith, Rhode Island. In November, 18 of 32 fish examined contained parasites, and in March, 91 of 232. The worms were larger and more numerous in the fall. When first isolated, E. gadi consumed oxygen at 9.65 μmoles/g-hr at 25 C, and during 10 days of survival outside the host (at 5 C) the rate diminished to less than half the initial rate. Respiratory quotient, initially 0.78, rose in 2 days to near 1.0, and remained there. Oxygen consumption was unaffected by 0.002–0.200 m glucose, 0.120 m succinate, or 0.150 m alanine. Under nitrogen, the worms produced acid, which was measured as carbon dioxide released from a medium containing bicarbonate; the rate was 6.12 μmoles CO 2/g-hr. Addition of glucose (0.035 m) increased acid production 40%. Glucose- 14C at 0.32 m m was taken up at an initial rate of 3.79 μmoles/g-hr; the label appeared in lactic acid, and in all six of the citric acid cycle intermediates examined. After incubation with glucose- 14C for 3 hr, worms that were kept 12 hr. in aerated medium excreted labeled lactic acid almost exclusively, while those kept anaerobically produced nearly equal amounts of labeled succinic and lactic acids. Carbon dioxide fixation into succinic and other acids was demonstrated with labeled bicarbonate. Carbon dioxide fixation rates increased with total bicarbonate concentration of the medium, to a maximum of 1.20 μmoles CO 2/g-hr at 14.7 m m bicarbonate, or 12.5% of the O 2 consumption rate of freshly isolated worms. No uptake of aspartic acid was detected in 4 hr.

Multiple Transport Components for Dicarboxylic Amino Acids in Streptococcus faecalis

Abstract Kinetic studies of glutamic acid uptake in Streptococcus faecalis revealed the operation of two saturable transport components with widely different apparent Km values. While studying the properties of these systems, we investigated the possibility that one of these kinetic components was a metabolic system which led to the intracellular accumulation of substantial amounts of a glutamic acid metabolite. At either low or high extracellular glutamate concentrations in the operating range of either the high or low affinity components, between 81 and 86% of the accumulated isotope remained in glutamic acid during the first 2 min of uptake. The distribution of isotope among chromatographically separated intracellular glutamate metabolites was the same when glutamate was accumulated largely by either the high or the low affinity system indicating that neither kinetic component represents a metabolic system. This conclusion was supported by comparable findings using a mutant which lacks the high affinity transport component. Aspartic acid uptake also was characterized by curvilinear Lineweaver-Burk plots. Competition studies indicated that aspartic and glutamic acids are taken up by the same two kinetic components. The high affinity system showed an absolute dependence on glucose as judged by initial rate studies or equilibrium accumulation levels. Glucose dependence of the low affinity system could be demonstrated only after several minutes of uptake when a sizeable pool had been accumulated. In some cases glucose inhibited the initial rate of uptake by this component. No additional criteria for distinguishing the two dicarboxylic amino acid transport components were encountered other than a greater sensitivity to glutamine competition in the low affinity system. Kinetic studies of glutamine, α-aminoisobutyric acid, and cycloleucine transport revealed curvilinear Lineweaver-Burk plots in all cases. For glutamine and α-aminoisobutyrate, the observed kinetics could be accounted for by the operation of a saturable and a diffusion-controlled process. In contrast, cycloleucine transport appeared to involve two saturable components.