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PubMed1981

Amino acid transport in human lymphocytes: distinctions in the enhanced uptake with PHA treatment or amino acid deprivation.

Human blood lymphocytes increase their concentrative uptake of amino acids when treated with plant lectins such as phytohemagglutinin or when exposed to an amino acid deficient environment (adaptation). Previous studies of the PHA effect have been conducted principally with alpha-aminoisobutyric acid (AIB). We have studied the transport characteristics of naturally occurring amino acids by PHA-treated lymphocytes. These studies have been conducted in the absence and presence of added carrier amino acid to determine whether an increase in transport after PHA treatment is mediated by the same mechanism that occurs during adaptation to a low amino acid environment. PHA stimulated the uptake of AIB, alanine, and proline 1.5- to 2-fold after 4 hours' exposure. AIB and proline, but not alanine transport, also increased when lymphocytes were in an amino acid-deficit medium. When lymphocytes were in an amino acid-deficient medium with PHA, the increase in uptake induced by PHA was superimposed on the increase that occurred in response to an amino acid-deficient medium. Also, PHA stimulated a delayed increase (16--20 hours) in the transport of leucine, whose uptake does not adapt to an amino acid-deficient medium. These data suggest that PHA and amino acid deprivation stimulated rate increases in amino acid transport by separate mechanisms.

Amino Acids↗
PubMed2004

Transcellular transport of radioiodinated 3-iodo-alpha-methyl-L-tyrosine across monolayers of kidney epithelial cell line LLC-PK1.

OBJECTIVE: 3-[123I]iodo-alpha-methyl-L-tyrosine ([123I]IMT) is an imaging agent for amino acid transport. In order to obtain fundamental data related to tumor imaging with [123I]IMT and renal physiological accumulation of [123I]IMT, we investigated the transport characteristics of [125I]IMT in porcine kidney epithelial cell line LLC-PK1 using cell monolayers grown on microporous membrane filters. METHODS: LLC-PK1 monolayers were created on a collagen-coated microporous (3 microm) membrane (4.7 cm2). To examine transcellular transport (secretion and reabsorption) and accumulation, the monolayers were incubated for up to 90 min at 37 degrees C with 18.5 kBq [125I]IMT in Dulbecco's phosphate-buffered saline (pH 7.4) as an uptake solution. After incubation, transcellular transport was assessed by quantifying the radioactivity of the solutions on each side of the monolayer. For the accumulation experiment, the cells were solubilized in NaOH solution, and the radioactivity was quantified. For the inhibition experiment, the inhibitor was added at a final concentration of 1 mM. For the pH dependence experiment, the pH of the apical-side uptake solution was varied from pH 5 to pH 8. Transport of [14C]Tyr was examined for comparison. RESULTS: Bi-directional transcellular transport of [125I]IMT was observed, corresponding to secretion and reabsorption in proximal tubule. Accumulation of [125I]IMT from the basolateral side (1.62 +/- 0.15%) and the apical side (2.62 +/- 0.35%) was observed at 90 min. 2-Amino-bicyclo[2,2,1]heptane-2-carboxylic acid (a specific inhibitor of system L), L-Tyr (mother compound of [125I]IMT) and 2-aminoisobutyric acid (an inhibitor of system L and A) inhibited both directional transport (p < 0.01) and accumulation (p < 0.01). 2-(Methylamino)isobutyric acid (a specific inhibitor of system A) appeared to inhibit transport and accumulation, but the results were not significant. Decreasing apical pH significantly enhanced accumulation of [125I]IMT from both sides (p < 0.001), whereas accumulation of mother L-Tyr was significantly suppressed. CONCLUSIONS: The inhibition experiments suggest that the main contributor to [125I]IMT transport is system L, rather than Na+ -dependent transport, in both apical and basolateral membrane. [125I]IMT was transported by the system that transported L-Tyr, but the observed pH dependence of transport suggests that different mechanisms are involved in accumulation of [125I]IMT and [14C]Tyr.

Amino Acid Transport Systems↗
PubMed1988

Induction of conditioned taste aversion in rats by GABA or other amino acids.

GABA included in the diet is known to reduce food intake and growth of rats fed a low protein diet. Experiments were designed to determine if GABA or other small neutral amino acids would affect food intake if they were administered separately from the diet, and if such amino acids could induce a conditioned taste aversion (CTA) to saccharin. Intubated or injected GABA or alpha-aminoisobutyric acid (AIB), a non-metabolizable isomer of GABA, reduced food intake. When rats were fed a low protein diet, IP injection of threonine (2 mmoles/200 g rat) induced CTA but did not depress food intake; serine (3 mmoles/200 g rat) induced CTA and caused only a small reduction in food intake. Another isomer, alpha-amino-n-butyric acid did not affect food intake or induce CTA at the tested concentrations. Adaptation to a high protein diet, which increases enzymatic degradation of many amino acids including GABA and serine, lessened severity of GABA-induced CTA and eliminated that caused by serine. CTA to saccharin can be induced by certain amino acids; the mechanism is unknown but may involve malaise or other adverse sensations.

Amino Acids↗
PubMed1995

Early and transient increase of rat hippocampal blood-brain barrier permeability to amino acids during kainic acid-induced seizures.

The effects of kainic acid (KA) induced seizures on the permeability of hippocampal blood-brain barrier (BBB) to amino acids were investigated using a new method based on the combination of brain microdialysis of alpha-[3H]aminoisobutyric acid (AIB) and blood sampling. The transfer of AIB through the BBB was thus, for the first time, monitored in vivo in awake animals. KA administration i.v. produces a rapid and transient increase in hippocampal transfer of AIB after the beginning of seizures which is closely correlated to epileptic activity. The possible consequences of this increased transport of AIB from blood to brain are discussed in relation to previously reported transient augmentations of extracellular cerebral glutamate concentrations during KA-induced epilepsy.

Amino Acids↗
PubMed1971

Nonprotein amino acids in the murchison meteorite.

Twelve nonprotein amino acids appear to be present in the Murchison meteorite. The identity of eight of them has been conclusively established as N-methylglycine, beta-alanine, 2-methylalanine, alpha-amino-n-butyric acid, beta-amino-n-butyric acid, gamma-amino-n-butyric acid, isovaline, and pipecolic acid. Tentative evidence is presented for the presence of N-methylalanine, N-ethylglycine, beta-aminoisobutyric acid, and norvaline. These amino acids appear to be extraterrestrial in origin and may provide new evidence for the hypothesis of chemical evolution.

Journal Article↗
PubMed1992

Vasogenic brain edema induced by arachidonic acid: role of extracellular arachidonic acid in blood-brain barrier dysfunction.

The effects of free arachidonic acid on the capillary permeability of normal rat brains were studied by measuring the regional uptake of [14C]aminoisobutyric acid by a quantitative autoradiographic technique. Intracerebral infusion of sodium arachidonate increased capillary permeability in a dose-dependent manner up to a concentration of 2 mmol/L. A high dose of arachidonic acid (more than 5 mmol/L) produced marked tissue destruction around the injection site (needle track) and increased capillary permeability less than 2 mmol/L arachidonic acid did. A time-course study demonstrated that about 80% of the maximum increase in capillary permeability produced by arachidonic acid was observed within 2 hours after the infusion was initiated. In addition, capillary permeability gradually increased with time up to 24 hours, after which it declined to about half of the maximum increase 48 hours after infusion. These effects of arachidonic acid on capillary permeability were localized within about 1.6 mm around the injection site. Pretreatment with dexamethasone did not completely, but did significantly, inhibit the arachidonic acid-induced increase in capillary permeability. The inhibitory effect of dexamethasone was completely suppressed by the administration of actinomycin D, which inhibits de novo protein synthesis, 1 hour before the treatment with dexamethasone. These results suggest that arachidonic acid, which is released and accumulated in the extracellular space, increases the capillary permeability of the brain in at least two different ways. One is the direct action of the arachidonic acid itself, which can stimulate perturbation of the membrane of the capillary endothelial cells, thus promoting an increase in capillary permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

N tau-Ribosylhistidine, a novel histidine derivative in urine of histidinemic patients. Isolation, structure, and tissue level.

On amino acid analysis of urine of histidinemic patients, an unidentified compound was eluted in a position between beta-aminoisobutyric acid and gamma-aminobutyric acid. This compound was purified to homogeneity from the urine by a combination of extraction with 80% ethanol, repeated column chromatography on Bio-Rad AG-50, and high performance liquid chromatography on a strongly cationic ion exchanger. The compound yielded free histidine on hydrolysis in an evacuated sealed tube with 0.1-6.0 M HCl at 145 degrees C for 5 h, but not at 100 degrees C for 24 h. This compound was determined to be N tau-ribosylhistidine by 1H and 13C NMR spectroscopies. The urinary content of this material in normal and histidinemic children was 17.8 +/- 13.4 (n = 10) and 126 +/- 51 (n = 14) mumol/g creatinine (mean +/- S.D.), respectively, and were closely correlated with those of urinary histidine. The renal clearance value of N tau-ribosylhistidine in humans was 96% of that of creatinine. When rats were fed on diets rich in histidine, the urinary excretion of N tau-ribosylhistidine increased greatly and was well correlated with the intake of histidine.

Amino Acid Metabolism, Inborn Errors↗
PubMed1993

Fusion activity of an amphiphilic polypeptide having acidic amino acid residues: generation of fusion activity by alpha-helix formation and charge neutralization.

A sequential polypeptide, poly(Glu-Aib-Leu-Aib) (Aib represents 2-aminoisobutyric acid), was synthesized and the pH-dependence of fusogenic activity of the polypeptide was studied. The polypeptide was designed to take amphiphilic structure upon the formation of alpha-helix. Circular dichroism spectra of the polypeptide showed a negative Cotton effect with double minima, indicative of an alpha-helical conformation. The alpha-helix content was increased with lowering pH and/or increasing the ionic strength. It was found that the polypeptide induces remarkable leakage of calcein from egg-yolk phosphatidylcholine (EYPC) vesicles loaded in the inner aqueous phase with lowering pH and/or increasing ionic strength. The polypeptide caused fusion of EYPC liposomes and dipalmitoylphosphatidylcholine liposomes more strongly with decreasing pH. Moreover, two distinct increases of fusogenic activity of the polypeptide were observed near pH 6.0 and below pH 4.5. The former corresponds to the midpoint of pH-dependent change in helical content of the polypeptide and the latter the pKa of the gamma-carboxyl group of glutamic acid. These results indicate that elevation of the fusogenic activity of the polypeptide is related to the increase in two factors, alpha-helix content and hydrophobicity.

Amino Acid Sequence↗
PubMed2001

First crystallographic signature of amyloid-like fibril forming beta-sheet assemblage from a tripeptide with non-coded amino acids.

The model tripeptide Boc-beta-Ala(1)-Aib(2)-beta-Ala(3)-OMe 1 [beta-Ala: beta-alanine, Aib: alpha-aminoisobutyric acid] forms an infinite parallel beta-sheet structure through intermolecular interactions in single crystals and from the SEM diagram of this peptide, it is evident that the compound has fibrillar morphology, a characteristic of neurodegenerative disease causing amyloid aggregate.

Amino Acids↗
PubMed1977

Role of protein dissociation in the transport of acidic amino acids by the Ehrlich ascites tumor cell.

The pH profile for the uptake of L-glutamic acid by the Ehrlich ascites tumor cell arises largely as a sum of the decline with falling pH of a slow, Na+-dependent uptake by System A, and an increasing uptake by Na+-independent System L. The latter maximizes at about pH 4.5, following approximately the titration curve of the distal carboxyl group. This shift in route of uptake was verified by (a) a declining Na+-dependent component, (b) an almost corresponding decline in the 2-(methylamino)-isobutyric acid-inhibitable component, (c) a rising component inhibited by 2-aminonorbornane-2-carboxylic acid. Other amino acids recognized as principally reactive with Systems A or L yielded corresponding inhibitory effects with some conspicious exceptions: 2-Aminoisobutyric acid and even glycine become better substrates of System L as the pH is lowered; hence their inhibitory action on glutamic acid uptake is not lost. The above results were characterized by generally consistent relations among the half-saturation concentrations of the interacting amino acids with respect to: their own uptake, their inhibition of the uptake, one by another, and their trans stimulation of exodus, one by another. A small Na+-dependent component of uptake retained by L-glutamic acid but not by D-glutamic acid at pH 4.5 is inhibitable by methionine but by neither 2-(methylamino)-isobutyric acid nor the norbornane amino acid. We provisionally identified this component with System ASC, which transports L-glutamine throughout the pH range studied. No transport activity specific to the anionic amino acids was detected, and the unequivocally anionic cysteic acid showed neither significant mediated uptake nor inhibition of the uptake of glutamic aic or of the norbornane amino acid. The dicarboxylic amino acids take the sequence, aspartic acid less than glutamic acid less than alpha-aminoadipic acid less than S-carboxymethylcysteine, in their rate of mediated, Na+-independent uptake at low pH. Diiodotyrosine and two dissimilas isomers of nitrotyrosine also show acceleration of uptake as the phenolate group on the sidechain is protonated, a result indicating that the acidic group need not be a carboxyl group and need not take a specific position in space to be accepted at the receptor site L. The presence of the carboxyl group does not upset the normal stereospecificity of System L until it falls on the beta-carbon in aspartic acid; even then it is the presence of the carbonyl group and not of the intact carboxyl group nor of its hydroxyl group that cancels out the stereospecificity, as was shown by the absence of normal stereospecificity for aspartic acid and asparagine and its presence in glutamic acid, homoserine and glutamine. In agreement, the uptak of aspartic acid is peculiarly sensitive to the presence of an alpha-methyl group or of other structures that modify the orientation of the sidechain.

Amino Acids↗
PubMed1991

Evidence for coordinate regulation of the A system for amino acid transport and the mRNA for the alpha 1 subunit of the Na+,K(+)-ATPase gene in Chinese hamster ovary cells.

Previous work suggested that the structural gene for the A system transporter and the mRNA for the alpha subunit of the Na+,K(+)-ATPase in Chinese hamster ovary cells CHO-K1 [wild type (WT)] are coordinately controlled by regulatory gene R1. This conclusion was based on analysis of a mutant for the A system, alar4. This mutant had a constitutive level of A system transport activity equal to the level found in derepressed WT cells and a 4 times increase in abundance of the alpha 1 subunit of Na+,K(+)-ATPase mRNA over that found in repressed WT. The level of Na+ per cell in alar4 was not significantly greater than that found in the WT. To further characterize the likely coregulation of both genes, we have studied the A system activity and Na+,K(+)-ATPase mRNA alpha 1-subunit levels in cells grown under various conditions that result in repression or derepression of the A system in the WT. System A activity increased up to 2-3 times the basal transport rate (repressed state) and Na+,K(+)-ATPase mRNA alpha 1-subunit levels showed a 3-fold increase after amino acid starvation (derepressed state). These changes occurred along with a decrease in intracellular Na+ levels. N-Methyl-alpha-aminoisobutyric acid and beta-alanine, previously shown to be corepressors for the A system, prevented to a similar extent A system derepression and Na+,K(+)-ATPase mRNA alpha 1-subunit accumulation. On the other hand, phenylalanine and lysine, amino acids that are not corepressors of the A system, failed to significantly prevent derepression of both genes. Hybrids between the WT and alar4 have the phenotype of the WT when grown under repressed conditions. These results give further support to the proposition that both the A system transporter and mRNA for the alpha 1 subunit of the Na+,K(+)-ATPase are coordinately controlled by regulatory gene R1 and elevated Na+ concentrations are not involved. No Na+,K(+)-ATPase activity was detected in derepressed cells. Activity was restored by the addition of monensin. However, this activity was no greater than that obtained in repressed cells. Indications are that the reduced Na+ content in derepressed cells inhibits Na+,K(+)-ATPase activity and that conditions that favored derepression do not allow for de novo synthesis of the Na+,K(+)-ATPase.

Alanine↗
PubMed2004

Taurine-induced long-lasting potentiation in the rat hippocampus shows a partial dissociation from total hippocampal taurine content and independence from activation of known taurine transporters.

Perfusion with high millimolar levels of taurine evoked a long-lasting potentiation (LLP-TAU) of synaptic transmission in the Schaffer-collateral CA1 region of the rat hippocampus. Although LLP-TAU showed some correlations to increases in the total taurine content of hippocampal slices, it could not be blocked by the taurine transport inhibitor guanidinoethanesulfonic acid (GES), which was able to significantly reduce total slice taurine uptake. Inhibition of GABA transport by either nipecotic acid or beta-guanidinopropionate failed to abolish LLP-TAU and had no significant effect on taurine uptake. The combination of GES and nipecotic acid also had no significant effect on LLP-TAU. Experiments with transportable structural analogs of taurine (beta-aminoisobutyric acid, homotaurine, and isethionic acid) suggest that activation of classical taurine transport pathways does not always yield a robust LLP-TAU. Hippocampal LLP-TAU could be significantly attenuated, however, by pre-incubation with submillimolar levels of taurine. In summary, the development of LLP-TAU in the rat hippocampus appears to be associated with the intracellular accumulation rather than the activation of known transporters of taurine, but the precise means of its accumulation remains to be identified.

Animals↗
PubMed1996

Isolation of a cDNA encoding a taurine transporter in the human retinal pigment epithelium.

Reverse transcription-polymerase chain reaction (RT-PCR) was performed to amplify a cDNA encoding a taurine transporter in the human retinal pigment epithelium (HRPE). The coding region of a PCR product was found to be 1863 bp long, predicting a 620-amino acid protein (69,826 Da). This cDNA sequence is almost identical to those taurine transporters recently determined in the human thyroid and placenta: 12 and 1 base pair(s) different from the reported thyroid and placenta transporter clones, respectively. The injection of mRNA in vitro transcribed from the PCR product markedly increased taurine uptake in Xenopus laevis oocytes. Taurine uptake is Na+ and Cl- dependent. Unlabeled taurine, beta-alanine and gamma-amino-n-butyric acid at 100 microM inhibited the uptake of radiolabeled taurine whereas 100 microM alpha-alanine and alpha-aminoisobutyric acid did not. A kinetic study showed that taurine uptake is mediated by a single carrier system with the apparent Michaelis-Menten constant of approximately 2 microM. These results suggest that the PCR product encodes a functional taurine transporter whose characteristics are similar to those of taurine uptake observed in the original HRPE cells. A DNA encoding the reported placental transporter was made from the PCR product by site-directed mutagenesis but it was not functional in the oocyte expression. A similar RT-PCR was performed with poly (A)+ mRNA isolated from JAR human placenta choriocarcinoma cells. This PCR product was identical to that from the HRPE. In addition, the clone of the human thyroid transporter was obtained and re-sequenced. Its translation coding region was also identical to that of the PCR product from the HRPE, showing that taurine transporters are identical in the human RPE, thyroid and placenta.

Amino Acid Sequence↗
PubMed1995

A search for endogenous amino acids in the Martian meteorite EETA79001.

The Antarctic shergottite EETA79001 is believed to be an impact-ejected fragment of the planet Mars. Samples of the carbonate (white druse) and the basaltic (lithology A) components from this meteorite have been found to contain amino acids at a level of approximately 1 ppm and 0.4 ppm, respectively. The detected amino acids consist almost exclusively of the L-enantiomers of the amino acids commonly found in proteins, and are thus terrestrial contaminants. There is no indication of the presence of alpha-aminoisobutyric acid, one of the most abundant amino acids in several carbonaceous chondrites. The relative abundances of amino acids in the druse material resemble those in Antarctic ice, suggesting that the source of the amino acids may be ice meltwater. The level of amino acids in EETA79001 druse is not by itself sufficient to account for the 600-700 ppm of volatile C reported in druse samples and suggested to be from endogenous martian organic material. However, estimates of total terrestrial organic C present in the druse material based on our amino acid analyses and the organic C content of polar ice can account for most of the reported putative organic C in EETA79001 druse.

Amino Acids↗
PubMed1985

Peptide sweeteners. 8. Synthesis and structure-taste relationship studies of L-aspartyl-D-alanyl tripeptides.

Several L-aspartyl-D-alanyl tripeptides have been synthesized to investigate the structural requirements of the C-terminal amino acid needed to elicit a taste response. Following our suggestion that a rigid, hydrophobic residue is required, both alpha, alpha-dialkane and cycloalkane alpha-amino acid methyl esters were incorporated into the tripeptide. The L-aspartyl-D-alanine-based tripeptide derivatives of alpha-aminoisobutyric acid methyl ester, alpha, alpha-diethylglycine methyl ester, and alpha-aminocycloalkanecarboxylic acid methyl esters from three- to six-membered rings are sweet. The higher analogues of the cycloalkane series containing alpha-aminocycloheptanecarboxylic acid methyl ester and alpha-aminocyclooctanecarboxylic acid methyl ester are bitter. It is important to note that this series of tripeptides (analogous to the previously reported dipeptides) goes from sweet to bitter to tasteless as the ring size of the C-terminal amino acid increases. The relationships between effective volume of the C-terminal residue, size requirements of the sweet receptor, and taste are discussed.

Motion↗
PubMed2000

Identification and characterization of a Na(+)-independent neutral amino acid transporter that associates with the 4F2 heavy chain and exhibits substrate selectivity for small neutral D- and L-amino acids.

A cDNA was isolated from the mouse brain that encodes a novel Na(+)-independent neutral amino acid transporter. The encoded protein, designated as Asc-1 (asc-type amino acid transporter 1), was found to be structurally related to recently identified mammalian amino acid transporters for the transport systems L, y(+)L, x(C)(-), and b(0,+), which are linked, via a disulfide bond, to the type II membrane glycoproteins, 4F2 heavy chain (4F2hc), or rBAT (related to b(0,+) amino acid transporter). Asc-1 required 4F2hc for its functional expression. In Western blot analysis in the nonreducing condition, a 118-kDa band, which seems to correspond to the heterodimeric complex of Asc-1 and 4F2hc, was detected in the mouse brain. The band shifted to 33 kDa in the reducing condition, confirming that Asc-1 and 4F2hc are linked via a disulfide bond. Asc-1-mediated transport was not dependent on the presence of Na(+) or Cl(-). Although Asc-1 showed a high sequence homology (66% identity at the amino acid level) to the Na(+)-independent broad scope neutral amino acid transporter LAT2 (Segawa, H., Fukasawa, Y., Miyamoto, K., Takeda, E., Endou, H., and Kanai, Y. (1999) J. Biol. Chem. 274, 19745-19751), Asc-1 also exhibited distinctive substrate selectivity and transport properties. Asc-1 preferred small neutral amino acids such as Gly, L-Ala, L-Ser, L-Thr, and L-Cys, and alpha-aminoisobutyric acid as substrates. Asc-1 also transported D-isomers of the small neutral amino acids, in particular D-Ser, a putative endogenous modulator of N-methyl-D-aspartate-type glutamate receptors, with high affinity. Asc-1 operated preferentially, although not exclusively, in an exchange mode. Asc-1 mRNA was detected in the brain, lung, small intestine, and placenta. The functional properties of Asc-1 seem to be consistent with those of a transporter subserving the Na(+)-independent small neutral amino acid transport system asc.

Amino Acid Sequence↗
PubMed1976

Amino acid uptake by fetal kidney slices.

Kidney slices of 7-17-week-old human fetuses were incubated for 90 min or less in Krebs-Ringer solution containing aminoisobutyric acid (AIB). Cell to medium ratios of AIB decrease with increasing fetal age. Uptake rate is slower than for mature human tissue. Both water content and extracellular space is high in embryonic tissue as compared to adult.

Age Factors↗
PubMed1977

Third system for neutral amino acid transport in a marine pseudomonad.

Uptake of leucine by the marine pseudomonad B-16 is an energy-dependent, concentrative process. Respiratory inhibitors, uncouplers, and sulfhydryl reagents block transport. The uptake of leucine is Na+ dependent, although the relationship between the rate of leucine uptake and Na+ concentration depends, to some extent, on the ionic strength of the suspending assay medium and the manner in which cells are washed prior to assay. Leucine transport can be separated into at least two systems: a low-affinity system with an apparent Km of 1.3 X 10(-5) M, and a high-affinity system with an apparent Km of 1.9 X 10(-7) M. The high-affinity system shows a specificity unusual for bacterial systems in that both aromatic and aliphatic amino acids inhibit leucine transport, provided that they have hydrophobic side chains of a length greater than that of two carbon atoms. The system exhibits strict stereospecificity for the L form. Phenylalanine inhibition was investigated in more detail. The Ki for inhibition of leucine transport by phenylalanine is about 1.4 X 10(-7) M. Phenylalanine itself is transported by an energy-dependent process whose specificity is the same as the high-affinity leucine transport system, as is expected if both amino acids share the same transport system. Studies with protoplasts indicate that a periplasmic binding protein is not an essential part of this transport system. Fein and MacLeod (J. Bacteriol. 124:1177-1190, 1975) reported two neutral amino acid transport systems in strain B-16: the DAG system, serving glycine, D-alanine, D-serine, and alpha-aminoisobutyric acid; and the LIV system, serving L-leucine, L-isoleucine, L-valine, and L-alanine. The high-affinity system reported here is a third neutral amino acid transport system in this marine pseudomonad. We propose the name "LIV-II" system.

Amino Acids↗