Regulation Of Amino Acid Uptake Research Articles

Asparagine promotes cancer cell proliferation through use as an amino acid exchange factor.

Cellular amino acid uptake is critical for mTOR complex 1 (mTORC1) activation and cell proliferation. However, the regulation of amino acid uptake is not well-understood. Here we describe a role for asparagine as an amino acid exchange factor: intracellular asparagine exchanges with extracellular amino acids. Through asparagine synthetase knockdown and altering of media asparagine concentrations, we show that intracellular asparagine levels regulate uptake of amino acids, especially serine, arginine and histidine. Through its exchange factor role, asparagine regulates mTORC1 activity and protein synthesis. In addition, we show that asparagine regulation of serine uptake influences serine metabolism and nucleotide synthesis, suggesting that asparagine is involved in coordinating protein and nucleotide synthesis. Finally, we show that maintenance of intracellular asparagine levels is critical for cancer cell growth. Collectively, our results indicate that asparagine is an important regulator of cancer cell amino acid homeostasis, anabolic metabolism and proliferation.

Uptake of intact amino acids by plants depends on soil amino acid concentrations

Studies in different ecosystems have shown that plants take up intact amino acids directly but little is known about the influence of free amino acid concentrations in the soil on this process. We investigated the effect of three different soil amino acid N concentrations (0.025, 0.13 and 2.5 μg N g −1 soil) on direct uptake of four dual labelled ( 15N, 13C) amino acids (glycine, tyrosine, lysine, valine) in a greenhouse experiment using Anthoxantum odoratum as a model plant. Our results revealed that 8–45% of applied 15N was incorporated into plant root and shoot tissue 48 h after labelling. Additional 13C enrichment showed that 2–70% of this incorporated 15N was taken up as intact amino acid. Total 15N uptake and 15N uptake as intact amino acids were significantly affected by soil amino acid N concentrations and significantly differed between the four amino acids tested. We found a positive effect of soil amino acid concentrations on uptake of mineralized 15N relative to amino acid concentrations for all amino acids which was presumably due to higher diffusion rates of mineralized tracer to the root surface. However, intact amino acid uptake relative to amino acid concentrations as well as the proportion of total 15N taken up directly decreased with increasing soil amino acid N concentrations for all amino acids, irrespective of their microbial degradability. This effect is most likely controlled by the mineral N concentration in soil and perhaps in plants which inhibits direct amino acids uptake. Overall, we conclude that plant internal regulation of amino acid uptake controlled by mineral N is the main mechanism determining direct uptake of amino acids and thus a lower contribution of intact amino acid uptake to the plants N nutrition has to be expected for higher amino acid concentrations accompanied by mineralization in soil.

The Tsc/Rheb signaling pathway controls basic amino acid uptake via the Cat1 permease in fission yeast

The Tsc/Rheb signaling pathway plays critical roles in the control of growth and cell cycle. Studies in fission yeast have also implicated its importance in the regulation of amino acid uptake. Disruption of tsc2+, one of the tsc+ genes, has been shown to result in decreased arginine uptake and resistance to canavanine. A similar effect is also seen with other basic amino acids. We have identified a permease responsible for the uptake of basic amino acids by genetic complementation and disruption. SPAC869.11 (termed Cat1 for cationic amino acid transporter) contains 12 predicted transmembrane domains and its overexpression in wild type fission yeast leads to the increased uptake of basic amino acids and sensitivity to canavanine. Disruption of cat1+ in the deltatsc2 background interfered with the suppression of the canavanine-resistant phenotype of Atsc2 mutants by a dominant negative Rheb. In deltatsc2 mutant strains, the amount of Cat1 was not altered, but instead was mislocalized. This mislocalization was suppressed by the expression of dominant negative Rheb. In addition, we found that the loss of the E3 ubiquitin ligase, Pub1, also restores proper localization. These results provide a crucial link between Tsc/Rheb signaling and the regulation of the basic amino acid permease in fission yeast.

Four permeases import proline and the toxic proline analogue azetidine-2-carboxylate into yeast.

We have found that proline and the toxic proline analogue azetidine-2-carboxylate (AzC) are efficiently imported into Saccharomyces cerevisiae cells by four amino acid permeases, including two nitrogen-regulated permeases (PUT4 and GAP1) and two permeases that are regulated by the SPS sensor of extracellular amino acids (AGP1 and GNP1). In contrast to Agp1p, Gnp1p is not functionally expressed when cells are grown on media containing proline as sole nitrogen source. These findings have implications for the interpretation of studies using AzC to characterize nitrogen source-dependent regulation of amino acid uptake and of post-Golgi targeting and localization of amino acid permeases in yeast.

Regulation of amino acid uptake by carbon and nitrogen in Pinus sylvestris.

The simultaneous uptake of 13 different amino acids by Scots pine ( Pinus sylvestris L.) was characterized and its regulation investigated after pre-treatments with a range of C and N metabolites. The uptake system exhibited a broad substrate specificity, acquiring all tested amino acids at similar uptake rates. Uptake of all tested amino acids by excised roots was linear over a time period of 150 min and exhibited pH-dependency, showing a peak at pH 4.0-5.0. Uptake was increased following pre-treatments with glucose and sucrose, while ammonium pre-treatments had a negative effect on amino acid acquisition. Pre-treatments with the important Krebs cycle intermediates oxaloacetate or 2-oxoglutarate did not result in altered amino acid uptake. It is speculated that the up-regulation of uptake may be due to an increased flow of glucose through a sensor mechanism, such as hexokinase. The regulation of transport by N and C suggests a function for amino acid uptake in the N nutrition of the plant, thus further highlighting the importance of organic nitrogen for plant N nutrition suggested by an increasing amount of research.

Regulation of amino acid uptake in conifers by exogenous and endogenous nitrogen.

Although an accumulating amount of research clearly indicates that plants are capable of taking up exogenous amino acids, the actual importance of such organic N sources for plant N nutrition is under debate. In this study, we show that amino acid uptake by Scots pine (Pinus sylvestris L.) is significantly decreased by elevated internal NH(4)(+) levels, while it increases following exposure to exogenous amino acids. Furthermore, amino acid uptake is larger in N-deficient plants than in plants grown with a large access of N. The regulatory pattern of amino acid uptake shows important similarities to the regulation of NO(3)(-) and NH(4)(+) transport as well as to the regulation of yeast amino acid transporters. In addition, our data suggest that uptake may be regulated by factors not originating from N metabolism. The up-regulation of uptake in response to N deficiency suggests that amino acid uptake may be a significant contributor to the N economy of P. sylvestris.

Perspectives on ruminant nutrition and metabolism. II. Metabolism in ruminant tissues

The discovery of the dominance of short-chain fatty acids as energy sources in the 1940s and 1950s, as discussed in part I of this review (Annison & Bryden, 1998) led to uncertainties concerning the interrelationships of glucose and acetate in ruminant metabolism. These were resolved in the following decade largely by use of 14C-labelled substrates. Although only small amounts of glucose are absorbed in most dietary situations, glucose availability to ruminant tissues as measured by isotope dilution was shown to be substantial, indicating that gluconeogenesis is a major metabolic activity in both fed and fasted states. Studies with 14C-labelled glucose and acetate revealed that in contrast to non-ruminants, acetate and not glucose is the major precursor of long-chain fatty acids in ruminant tissues. Interest in the measurement of energy metabolism in livestock grew rapidly from the 1950s. Most laboratories adopted indirect calorimetry and precise measurements of the energy expenditure of ruminants contributed to the development of new feeding systems. More recently, alternative approaches to the measurement of energy expenditure have included the use of NMR spectroscopy, isotope dilution and the application of the Fick principle to measure O2 consumption in the whole animal and in defined tissues. The refinement of the classical arterio-venous difference procedure in the study of mammary gland metabolism in the 1960s, particularly when combined with isotope dilution, encouraged the use of these methods to generate quantitative data on the metabolism of a range of defined tissues. The recent introduction of new methods for the continuous monitoring of both blood flow and blood O2 content has greatly increased the precision and scope of arterio-venous difference measurements. The impact of data produced by these and other quantitative procedures on current knowledge of the metabolism of glucose, short-chain fatty acids and lipids, and on N metabolism, is outlined. The role of the portal-drained viscera and liver in N metabolism is discussed in relation to data obtained by the use of multi-catheterized animals. Protein turnover, and the impact of stress (physical, social and disease related) on protein metabolism have been reviewed. The growth of knowledge of mammary gland metabolism and milk synthesis since the first quantitative studies in the 1960s has been charted. Recent findings on the regulation of amino acid uptake and utilization by the mammary gland, and on the control of milk secretion, are of particular interest and importance.

Sodium ion-dependent (N-methylamino)-alpha-isobutyric [correction of isobutryic] acid uptake by embryonic chick cells exposed to ethanol in ovo:response to the stimulation/downregulation of protein kinases.

Amino acid uptake, critical for embryonic development, was studied in cultured chick cells isolated from 5-day-old chick embryos that had received treatment in ovo with either vehicle (sterile chick Ringer's solution) or vehicle plus ethanol (1.5 g/kg). Upon being placed in culture, the cells were grown in the absence of ethanol per se. The uptake of (N-methylamino)-alpha-isobutyric [correction of isobutryic] acid (AIB) was used to estimate amino acid uptake via system A, a Na+-dependent system that transports short-chain amino acids. The uptake of AIB in cultured chick embryo cells in response to the stimulation/downregulation of three protein kinases [tyrosine kinase, cyclic AMP-dependent kinase A (PKA) and protein kinase C (PKC)] was determined. Acute activation of PKC by treatment of the cells with a phorbol ester (TPA) inhibited Na+-dependent AIB uptake. Conversely, treatment of the cells with TPA for 24 h, to downregulate PKC activity, significantly increased AIB uptake. The data suggest that in these cells, PKC plays an important role in the regulation of amino acid uptake via system A. Activation of PKA via treatment of the cells with forskolin, an adenylyl cyclase activator, had little effect on AIB uptake in cells from vehicle-treated embryos and only a slight depressing effect on uptake by cells from ethanol-treated embryos. Insulin and insulin-like growth factor-1 (IGF-1) both stimulated AIB uptake, but the higher concentrations of insulin necessary to increase uptake to a level comparable to that of IGF-1 stimulation suggested that insulin could be acting through the IGF-1 receptor. Thus, while AIB uptake by cells of in ovo ethanol-treated embryos was significantly increased by treatment with either insulin or IGF-1, IGF-1 appeared to be the more physiologically important compound in the chick embryo. Overall, there was a consistent trend for cells isolated from in ovo ethanol-treated embryos to have higher levels of AIB uptake relative to cells isolated from vehicle-treated embryos, regardless of the in vitro treatment.

Follicle Cell Regulation of Amino Acid Uptake and Polyphosphoinositide Metabolism in Oocytes of the Limpet Patella vulgata

We investigated the role of follicle cells during meiosis reinitiation in the oocytes of Patella vulgata. Germinal vesicle breakdown, chromosome condensation, and metaphase-1 spindle formation were artificially induced by treating oocytes with 10 m M NH 4Cl. By following the accumulation of 32PO 4 and [ 3H]inositol in polyphosphoinositides (PPI) and by measuring chemical amounts of these lipids, we found that the presence of follicle cells caused PPI turnover to remain at a low level in the immature oocyte. On the other hand, the presence of these cells was necessary for maximal activation of the metabolism of these lipids during maturation. We also examined the nutritive role of follicle cells by studying the transport of leucine and found that the presence of these cells was necessary for optimal transport of this amino acid. We conclude that follicle cells can exert either a stimulatory or an inhibitory effect on the oocyte metabolism according to its state of maturity.

Effects of beta-blockade on hepatic conversion of amino acid nitrogen and on urea synthesis in cirrhosis

β-Blockers are widely used to prevent gastrointestinal hemorrhage in cirrhosis. The metabolic effects of treatment are scarcely studied: hepatic function reportedly does not change significantly, but β-adrenoceptors have been reported to regulate protein and amino acid metabolism. We studied hepatic nitrogen metabolism in response to constant alanine infusion in seven patients with cirrhosis before and 7 to 10 days after treatment with oral propranolol (60 to 100 mg/d). Beta-blockade was effective: it decreased heart rate by 25%, abolished orthostatic tachycardia, and reduced portal blood flow by 20%. Alanine-stimulated urea nitrogen synthesis rate (UNSR) was higher in patients with propranolol treatment, without any difference in aminonitrogen concentration. The kinetics of hepatic conversion of amino acid nitrogen into urea—ie, functional hepatic nitrogen clearance (FHNC)—increased by 30%, from (mean ± SD) 17.0 ± 4.1 to 22.0 ± 6.6 L/h ( P < .01). Increased urea production during alanine infusion resulted in negative nitrogen exchange even at the peak of α-aminonitrogen concentration. Basal insulin level was only slightly reduced during propranolol treatment, whereas the insulin response to alanine was significantly blunted. No differences in glucagon and cortisol were demonstrated. Epinephrine and norepinephrine levels were high-normal and did not vary after treatment. Increased urea production and stimulation of hepatic nitrogen clearance during beta-blockade may be mediated by relative hypoinsulinemia or by direct involvement of β-adrenoceptors in the control of nitrogen metabolism, possibly by regulation of amino acid uptake and release in peripheral tissues.

Amino acid transporters of lower eukaryotes: regulation, structure and topogenesis

Lower eukaryotes such as the yeast Saccharomyces cerevisiae and the filamentous fungus Aspergillus nidulans possess a multiplicity of amino acid transporters or permeases which exhibit different properties with respect to substrate affinity, specificity, capacity and regulation. Regulation of amino acid uptake in response to physiological conditions of growth is achieved principally by a dual mechanism; control of gene expression, mediated by a complex interplay of pathway-specific and wide-domain transcription regulatory proteins, and control of transport activities, mediated by a series of protein factors, including a kinase, and possibly, by amino acids. All fungal and a number of bacterial amino acid permeases show significant sequence similarities (33-62% identity scores in binary comparisons), revealing a unique transporter family conserved across the prokaryotic-eukaryotic boundary. Prediction of the topology of this transporter family utilizing a multiple sequence alignment strongly suggests the presence of a common structural motif consisting of 12 alpha-helical putative transmembrane segments and cytoplasmically located N- and C-terminal hydrophilic regions. Interestingly, recent genetic and molecular results strongly suggest that yeast amino acid permeases are integrated into the plasma membrane through a specific intracellular translocation system. Finally, speculating on their predicted structure and on amino acid sequence similarities conserved within this family of permeases reveals regions of putative importance in amino acid transporter structure, function, post-translational regulation or biogenesis.

Regulation of amino acid uptake into cerebral microvessels.

The carrier-mediated transport systems, found in cerebral endothelium, are responsible for maintaining the nutrient milieu of the CNS. The objective of this study was to identify what factors might regulate the sodium-dependent A-system of neutral amino acid transport in isolated cerebral microvessels. The uptake of amino acids into isolated microvessels was measured using methylaminoisobutyric acid (MeAIB) a nonhydrolyzable A-analog of the A-system carrier. The results indicated that stimulation of adrenergic (both alpha and beta) receptors significantly (P less than 0.05-0.02) increased the uptake of MeAIB. While the muscarinic agonist carbachol alone did not alter the uptake of MeAIB, it blocked the stimulation evoked by adrenergic agonists. Furthermore, addition of the metal ion, aluminum also significantly (P less than 0.05) increased specific uptake of MeAIB by 95%, when compared to untreated controls. These results indicate that the uptake of neutral amino acids, through the A-system, into cerebral microvessels, can be modulated by adrenergic and cholinergic receptors, as well as the metal ion aluminum. Since the A-system of amino acid transport may control appropriate levels of amino acids in brain, modulation of the uptake of amino acids by adrenergic and cholinergic receptors and by aluminum, may be associated with an imbalance of amino acids and possible neurotransmitter defects in the CNS.

Regulation of amino acid uptake by phorbol esters and hypertonic solutions in rat thymocytes.

Growth factors, mitogens, and malignant transformation can alter the rate of amino acid uptake in mammalian cells. It has been suggested that the effects of these stimuli on proliferation are mediated by activation of Na+/H+ exchange. In lymphocytes, Na+/H+ exchange can also be activated by phorbol esters and by hypertonic media. To determine the relationship between the cation antiport and amino acid transport, we tested the effects of these agents on the uptake of alpha-aminoisobutyric acid (AIB), methyl-AIB, proline, and leucine in rat thymocytes. Both 12-O-tetradecanoylphorbol-13-acetate (TPA) and hypertonicity stimulated amino acid uptake through system A (AIB, proline, and methyl-AIB). In addition, TPA, but not hypertonicity, also elevated leucine uptake. The stimulation of the Na+ -dependent system A was not due to an increased inward electrochemical Na+ gradient. The effects of TPA and hypertonic treatment were not identical: Stimulation of AIB uptake by TPA was observed within minutes, whereas at least 1 hr was required for the effect of hypertonicity to become noticeable. Moreover, stimulation by hypertonicity but not that by TPA, was partially inhibited by cycloheximide, suggesting a role of protein synthesis. That stimulation of Na+/H+ exchange does not mediate the effects on amino acid transport is suggested by two findings: 1) the stimulation of AIB uptake was not prevented by concentrations of amiloride or of 5-(N,N-disubstituted) amiloride analogs that completely inhibit the Na+/H+ antiport and 2) conditions that mimic the effect of the antiport, namely, increasing [Na+]i or raising pHi failed to stimulate amino acid uptake. Thus, in lymphocytes, activation of Na+/H+ exchange and stimulation of amino acid transport are not casually related.

Regulation of amino acid uptake and deoxyribonucleic acid synthesis in isolated human fetal fibroblasts and myoblasts: effect of human placental lactogen, somatomedin-C, multiplication-stimulating activity, and insulin.

We compared the abilities of human placental lactogen (hPL), somatomedin-C/insulin-like growth factor I (SM-C/IGF-I), multiplication-stimulating activity (MSA), and insulin to induce a rapid anabolic event, the uptake of the nonmetabolizable amino acid [3H]alpha-aminoisobutyric acid ([3H] AIB) or the more long term action of increasing [3H]thymidine incorporation, as a measure of DNA synthesis, in isolated human fetal fibroblasts and myoblasts. Myoblasts were derived from skeletal muscle and fibroblasts from skin explants removed from human fetuses delivered between 12 and 19 weeks gestation after prostaglandin-induced abortion. Each of the four peptides caused a dose-dependent increase in [3H]AIB uptake by both fibroblasts and myoblasts, with mean half-maximal concentrations (ED50) ranging from 0.9-1.9 nM. The concentration of each peptide required to stimulate [3H]thymidine uptake was significantly greater, with the exception of insulin, which was inactive. For myoblast cultures, the mean ED50 values were: hPL, 7.9 nM; SM-C/IGF-I, 2.0 nM; and MSA, 2.2 nM. For fibroblast cultures, the mean ED50 values were: hPL, 2.3 nM; SM-C/IGF-I, 3.3 nM; and MSA, 4.3 nM. Insulin did not stimulate [3H]thymidine incorporation into either cell type at concentrations up to 6.9 nM. Incubation in the presence of monoclonal antibody against SM-C/IGF-I abolished the ability of SM-C/IGF-I to stimulate either [3H]thymidine or [3H]AIB uptake into fetal fibroblasts. The antibody substantially inhibited the incorporation of [3H]thymidine by these cells in response to hPL, but was less effective in blocking hPL-stimulated [3H]AIB uptake. It did not inhibit the uptake of either radioisotope in response to MSA or [3H]AIB uptake in response to insulin. The actions of SM-C/IGF-I and hPL on thymidine incorporation were additive at submaximal concentrations, but not so at maximal individual concentrations. Their actions on AIB uptake were additive at both submaximal and maximal concentrations. The results suggest that hPL as well as the SMs may contribute to the growth stimulus in human fetal connective tissues. Since incubation with SM-C/IGF-I antibody reduced the mitogenic response of fetal cells to hPL, the actions on DNA synthesis may be partially mediated by local release of SM. However, the similar ED50 values with which these peptides stimulated [3H]AIB uptake during a short incubation, and their additive effects at maximal individual concentrations, suggest that hPL may also have direct actions.

Metabolic regulation of amino acid uptake in marine waters1

To determine the relationships among the processes of uptake, intracellular pool formation, and incorporation of amino acids into protein, we measured the uptake of dipeptides and free amino acids by bacterial assemblages in estuarine and coastal waters of the southeast U.S. The dipeptide phenylalanyl‐phenylalanine (phe‐phe) lowerd Vmax of phenylalanine uptake when the turnover rate of phenylalanine was relatively high. When the turnover rate was relatively low, phe‐phe either had no effect or increased Vmax of phenylalanine uptake. An analytical model was developed and tested to measure the turnover time of the intracellular pool of phenylalanine. When phe‐phe was not added the turnover time of the intracellular pool was 0.89 min. Addition of 1.0 nM phe‐phe increased the turnover time of this pool to 3.8 min in waters where phe‐phe lowered Vmax of phenylalanine uptake. These results suggested that the size of the intracellular pool is regulated, which precludes high assimilation rates of both phenylalanine and phe‐phe. In waters with relatively low phenylalanine turnover rates, bacterial assemblages appear to have a greater capacity to assimilate phenylalanine and phe‐phe simultaneously. Marine bacterial assemblages do not substantially increase the apparent respiration of amino acids when concentrations increase. We conclude that sustained increases in uptake rates and mineralization by marine bacterial assemblages in response to an increase in the concentration of dissolved organic nitrogen is determined by the rate of protein synthesis.

Gamma-glutamyl-amino acids as signals for the hormonal regulation of amino acid uptake by the mammary gland of the lactating rat.

The mammary gland is a good model to study the hormonal regulation of amino acid uptake. Danazol, which decreases gonadotrophin release, causes a fall in gamma-glutamyltranspeptidase (GGT) and in amino acid uptake by the gland. Treatment of the rats with estrogens and progesterone partially reverts this effect. Treatment with gonadotrophins completely reverts it. gamma-Glutamyl-amino acids (GAA) increase the uptake of amino acids by the mammary gland in rats previously treated with bromocriptine. We suggest that GAA may act as signals to stimulate amino acid uptake and that the role of GGT may be to generate that signal.

Amino acid transport in isolated rat hepatocytes.

Improvements in the collagenase perfusion techniques have made isolated rat hepatocytes a popular model in which to study hepatic function. Our knowledge of hepatic amino acid transport has been advanced as a result of this methodology. Translocation across the hepatocyte plasma membrane can, in some instances, represent the rate-limiting step in the overall metabolism of certain amino acids. Furthermore, regulation of amino acid uptake by hepatocytes appears to play a role in diabetes, and perhaps in malignant transformation. Comparisons between normal adult hepatocytes and several hepatoma cell lines show basic differences in amino acid transport. There are at least eight distinct systems in normal hepatocytes for transport of the hormones. Systems A and N exhibit enhanced uptake rates after the cells have been maintained in the absence of extracellular amino acids, a phenomenon termed adaptive control. Further studies using isolated hepatocytes will increase our basic understanding of membrane transport processes and their regulation.

Regulation of Amino Acid Uptake into Oat Mesophyll Cells: A Comparison between Protoplasts and Leaf Segments

The uptake of cc-aminoisobutyric acid (AIB) into protoplasts and into 1 cm sections of leaves from 7 d old light-grown oats (Avena sativa L. cv. 'Garry') was studied. Both protoplasts and leaf sections with cuticle and epidermis removed accumulated AIB against a concentration gradient although the rate of uptake into protoplasts was one-third to one-sixth that into leaf sections. AIB uptake into both protoplasts and leaf cells in situ was stimulated by 'aging,' and low pH, and inhibited by osmotic shock, respiratory poisons, and KC1 concentrations above 1 mM. It was concluded that the rate of uptake of AIB and its accumulation ratio could be accounted for by the energy inherent in the proton-motive force, the proton-motive force being the sum of the pH gradient and potential difference across the plasma membrane. The similarities between oat mesophyll protoplasts and leaf cells in situ suggest that these protoplasts are suitable material for the study of certain membrane-regulated events.

Regulation of amino acid uptake in lymphocytes stimulated by mitogens: I. Increase in AIB transport dependent on cell metabolism

1. 1. The dependence of the induction of the early increased rate of aminoisobutyric acid (AIB) transport on cell metabolism has been studied in rat lymphocytes stimulated by Concanavalin A (ConA). 2. 2. Inhibitors of energy generation such as dinitrophenol, KCN, NaF, oligomycin, and iodoacetate strongly inhibit the increase in the rate of AIB transport. The binding of 125I-labelled ConA to the rat lymphocyte is not affected by inhibitors of energy metabolism. 3. 3. Cycloheximide and puromycin strongly inhibit the early increase in the rate of AIB transport. Incubation with cycloheximide for a period of up to 150 min does not inhibit the rate of AIB transport in resting lymphocytes or the rate of AIB transport in already stimulated lymphocytes. 4. 4. Actinomycin D and mitomycin have no effect on the early increase in the rate of AIB transport. In the absence of an increase in RNA and DNA synthesis, half of the maximum stimulation of AIB transport and protein synthesis is obtained. 5. 5. It is concluded that the early increase in AIB transport is not caused by a simple interaction of ConA with the lymphocyte membrane. It requires participation of energy metabolism and protein synthesis but not of RNA or DNA synthesis.

Regulation of amino acid uptake by Euglena gracilis

Regulation of amino acid uptake by Euglena gracilis