The preparation and isolation of D-(-)-beta-aminoisobutyric acid.
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Amino Acids↗
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Transport of alpha aminoisobutyric acid into ocular fluids and lens.
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Amino Acids↗
The role of Na+ ions in the transport of alpha-aminoisobutyric acid and other amino acids into the lens.
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Amino Acids↗
Inhibition of hepatic uptake of alpha aminoisobutyric acid by ethanol: effects of pyrazole and metabolites of ethanol.
Ethanol inhibits the uptake of AIB by the isolated perfused rat liver. However, if the metabolism of ethanol is blocked by pyrazole, there is no reduction in accumulation of AIB by the liver. Acetaldehyde and acetate, metabolites of ethanol have no effect on AIB uptake by the liver. The inhibition of urea synthesis by ethanol is also prevented by pyrazole. Neither of the metabolites of ethanol inhibit urea synthesis in the isolated liver.
Acetaldehyde↗
Absorption kinetics for leucine, cycloleucine and alpha-aminoisobutyric acid by rat small intestine in vivo.
The intestinal absorption kinetics of three neutral amino acids, leucine, cycloleucine and alpha-aminoisobutyric acid, has been studied in rat jejunum in vivo, with luminal perfusion during successive periods, by measuring the passive component and the active transport. The mass-transfer coefficients of the passive process, are similar for the three amino acids and increase with the perfusion rate. The transport component, obtained from the difference between total absorption and passive diffusion, shows saturation kinetics and also increases with the perfusion rate. The apparent Michaelis constants, Km, and the maximal transport rates for the three amino acids have been determined. The Km values are greater than those reported for in vitro studies, a result imputable to greater thickness of the unstirred layers in vivo and to the unequal signification of the constant in both conditions. Passive flux has proved to be an important component for in vivo absorption, even at low substrate concentrations (1-5 mM), so that its evaluation cannot be neglected for the calculation ot the kinetic constants of the mediated transport.
Amino Acids↗
Postnatal intestinal maturation in rats: alpha-aminoisobutyric acid loss during in vivo, perfusion by hypertonic solutions.
We investigated with an in vivo single pass perfusion technique net secretion of [14C]aminoisobutyric acid, a non-metabolizable amino acid, from the proximal, distal small intestinal segments and from the colon segments of suckling (14-15 day old), weanling (21-22 day old) and adolescent (42-43 day old) rats during perfusion with either isotonic (300 mOsm/Kg) or hypertonic (500 mOsm/Kg) solutions. During isotonic perfusion, net secretion of [14C]aminoisobutyric acid was significantly greater in all segments of the suckling rats compared to corresponding values in segments of the adolescent rats. Rates of net secretion of [14C]aminoisobutyric acid in all segments of the weanling rats were intermediate between corresponding mean values of the suckling and adolescent rats. When secretion of [14C]aminoisobutyric acid was compared between individual segments, the colon was the major site of secretion followed by the proximal and then the distal segments in all age groups. During perfusion with hypertonic solutions there was significant increase in net secretion of [14C]aminoisobutyric acid in all segments of the suckling rats compared to mean values with isotonic perfusion. In the weanling and adolescent rats, there were no significant differences in the rates of net secretion of [14C]aminoisobutyric acid with hypertonic perfusion. Our findings suggests greater permeability of the intestinal epithelium not only to water, electrolytes and minerals but also to amino acids in the suckling rats compared to adolescent rats. The implication is that during periods of osmotic diarrhea infant animals appear to be at risk of losing amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)
Aminoisobutyric Acids↗
Evaluation of [1-11C]-alpha-aminoisobutyric acid for tumor detection and amino acid transport measurement: spontaneous canine tumor studies.
Alpha-aminoisobutyric acid (AIB), or alpha-methyl alanine, is a nonmetabolized amino acid transported into cells, particularly malignant cells, predominantly by the 'A' amino acid transport system. Since it is not metabolized, [1-11C]-AIB can be used to quantify A-type amino acid transport into cells using a relatively simple compartmental model and quantitative imaging procedures (e.g. positron tomography). The tissue distribution of [1-11C]-AIB was determined in six dogs bearing spontaneous tumors, including lymphosarcoma, osteogenic sarcoma, mammary carcinoma, and adenocarcinoma. Quantitative imaging with tissue radioassay confirmation at necropsy showed poor to excellent tumor localization. However, in all cases the concentrations achieved appear adequate for amino acid transport measurement at known tumor locations. The observed low normal brain (due to blood-brain barrier exclusion) and high (relative to brain) tumor concentrations of [1-11C]-AIB suggest that this agent may prove effective for the early detection of human brain tumors.
Amino Acids↗
Adaptive enhancement of amino acid transport in human leukemia leukocytes: studies with alpha-aminoisobutyric acid.
Initial rates of accumulation (Vi) of [3-14C] alpha-aminoisobutyric acid (AIB) by human leukemic leukocytes increased markedly and progressively during 240 minute incubations in amino acid-deficient media. Absolute increments were greater in blast cells from patients with acute lymphoblastic leukemia and with acute myeloblastic leukemia than in lymphocytes from patients with chronic lymphocytic leukemia, but per cent increments did not differ. Time-related increases appear to be restricted to an active mechanism for AIB entry and could not be attributed to cell damage, concomitant alterations in the incubation media, or progressive reduction in transinhibition of AIB entry. Studies with two cell populations revealed these increases to be associated with an augmented Vmax and a reduction in apparent Km, suggesting enhanced capacity and affinity of the transport system for AIB. Time-related increases failed to develop in two chronic lymphocytic leukemia (CLL) lymphocyte populations and were partially reduced in two leukemic blast cell populations during continuous exposure to high extracellular AIB concentrations. Hence, this phenomenon may represent an adaptive response to environmental amino acid deprivation. Adaptation may involve de novo protein and RNA synthesis, since it was not seen in cells which were treated with cycloheximide or actinomycin D. However, unlike previous observations in nonmalignant cells, once triggered, the adaptive response was not completely suppressed in leukemic cells which underwent a large degree of adaptation.
Acute Disease↗
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.
Amino Acids↗
Effects of NaCl on the uptake of alpha-[14C]aminoisobutyric acid by the halotolerant bacterium Halomonas elongata.
The alpha-aminoisobutyric acid (AIB) transport system of the halotolerant bacterium, Halomonas elongata, was examined. Cells were grown in L-alanine defined medium with 0.05, 0.375, 1.37, 2.5, or 3.4 M NaCl. Each group of cells was resuspended in buffered salts with different NaCl concentrations (0.05, 0.375, 1.37, 2.5, and 3.4 M) and the uptake of alpha-[14C]AIB was measured. Optimum AIB uptake occurred in the 0.375 M NaCl solution for the lower salt grown cells and the 1.37 M NaCl solution for the higher salt grown cells. When cells were grown in the higher salt media and suspended in hypoosmotic solutions, appreciable AIB uptake occurred; but for cells grown in lower salt media and suspended in hyperosmotic solutions, the uptake was dramatically reduced. This effect was mainly attributed to cell plasmolysis which in turn resulted in some cell death. The AIB uptake was Na+ specific and this analogue was not metabolized after being transported into the cells. An amino acid competition study gave a pattern similar to that of a marine bacterium.
Amino Acids↗
High excretion of beta-aminoisobutyric acid in patients with ketoacidosis.
High concentrations of beta-aminoisobutyric acid (BAIBA) were found to be present in the urine from patients with ketoacidosis. The R-form was always the dominating isomer of BAIBA. The finding is discussed, and it is suggested that the mechanism might be a derangement in the degradation of valine.
Acidosis↗
Sodium-stimulated alpha-aminoisobutyric acid transport by membrane vesicles from simian virus-transformed mouse cells.
Uptake of alpha-aminoisobutyric acid, by membrane vesicles derived principally from the plasma membrane and endoplasmic reticulum of mouse 3T3 cells transformed by simian virus 40, is stimulated by sodium chloride. Both in the presence and absence of Na+ uptake is time-dependent and osmotically sensitive. The Na+-stimulated uptake is inhibited by other amino acids. The kinetics of transport of alpha-aminoisobutyric acid are shown to be biphasic both in whole cells and in the membrane vesicles. Only the high affinity system is stimulated by sodium in the membrane vesicles. These results demonstrate that observations made on living cells correlate with observations made on isolated membrane vesicles, and indicate that these membrane vesicles have retained the cellular amino acid transport system functionally intact.
Amino Acids↗
Characteristics of an uptake system for alpha-aminoisobutyric acid in Leishmania tropica promastigotes.
Leishmania tropica promastigotes transport alpha-aminoisobutyric acid (AIB), the nonmetabolizable analog of neutral amino acids, against a substantial concentration gradient. AIB is not incorporated into cellular material but accumulates within the cells in an unaltered form. Intracellular AIB exchanges with external AIB. Various energy inhibitors (amytal, HOQNO, KCN, DNP, CCCP, and arsenate) and sulfhydryl reagents (NEM, pCMB, and iodoacetate) severely inhibit uptake. The uptake system is saturable with reference to AIB and the Lineweaver-Burk plots show biphasic kinetics suggesting the involvement of two transport systems. AIB shares a common transport system with alanine, cysteine, glycine, methionine, serine, and proline. Uptake is regulated by feedback inhibition and transinhibition.
Amino Acids↗
Urinary beta-aminoisobutyric acid excretion in thalassaemia.
The quantity of beta-aminoisobutyric acid (BAIB) excreted in the urine of patients with an intact spleen suffering from thalassaemia major appears to be proportional to the number of the circulating normoblasts and inversely proportional to the haemoglobin level. After splenectomy only minute amounts of BAIB are excreted. Transfusion constantly, but temporarily, reduces urinary excretion of beta-aminoisobutyric acid. Other anaemic but non-thalassaemic patients may excrete low levels.
Aminoisobutyric Acids↗
Identification of beta-aminoisobutyric acid in uremic serum.
An unidentified ninhydrin-positive substance found in uremic sera but not found in normal sera was isolated by gel-filtration through Sephadex G-75 followed by high voltage paper electrophoresis (pH 3.5), and identified as beta-aminoisobutyric acid using paper chromatography and automated amino acid analyzer. The quantitative determination of beta-aminoisobutyric acid in serum revealed that the level of beta-aminoisobutyric acid in uremic sera was much higher than that of normal sera. Gas chromatographic determination of the enantiomorphs of beta-aminoisobutyric acid showed that uremic sera contain R- and S-isomers of the amino acid, but with the R-isomer as the dominating form.
Aminoisobutyric Acids↗
The effects of ionizing radiation on the pulmonary endothelial cell uptake of alpha-aminoisobutyric acid and synthesis of prostacyclin.
The effects of gamma irradiation (150-3000 rad) on prostacyclin synthesis (PGI2) and Na+-dependent amino acid uptake (alpha-aminoisobutyric acid, AIB) were assessed in vitro in bovine pulmonary artery endothelial cells grown in plastic culture dishes. A dose-dependent increase in both PGI2 synthesis and AIB was found 24 h after irradiation at exposure levels greater than 600 rad. The increase in PGI2 synthesis [297% of sham-irradiated values at 3000 rad, P less than 0.01] was due to an increase in release of arachidonic acid from plasma membrane stores as well as stimulation of cyclooxygenase and/or prostacyclin synthetase enzymes. The increase in AIB uptake (75% increase at 3000 rad compared to sham-exposure values) correlated with the increased synthesis of PGI2 (r = 0.94). There was also a dose-dependent increase in the number of cells that became detached from the culture dishes during the 24-h period after irradiation. The changes in PGI2 synthesis and AIB uptake induced by gamma irradiation differed if the endothelial cells were grown on cover slips, indicating that the endothelial response to irradiation may be dependent on the interaction between the endothelial cell and its extracellular basement membrane matrix.
Aminoisobutyric Acids↗
Changes in transport of [14C] alpha-aminoisobutyric acid across the blood-brain barrier during pentylenetetrazol-induced status epilepticus in the immature rat.
In the present study, we measured the effects of pentylenetetrazol (PTZ)-induced status epilepticus on the blood-brain barrier (BBB) permeability in rats at postnatal age 10 (P10) or 21 days (P21). Seizures were induced by the repetitive injection of subconvulsive doses of PTZ until the onset of status epilepticus characterized as the loss of quadruped posture. The BBB permeability changes to the poorly diffusible amino acid [14C] alpha-aminoisobutyric acid (AIB) were measured by autoradiography at 10 min after the onset of status epilepticus. Seizures induced a generalized increase in BBB permeability to AIB that was significant in 22 and 26 regions out of the 34 studied at P10 and P21, respectively. Highest increases over control levels (> 250%) were recorded at both ages in interpeduncular nucleus, raphe nuclei and trigeminal nerve tractus. Quite high increases (> 150%) were recorded in cortical, inferior collicular and thalamic areas at P10 and in inferior colliculus, cerebellar cortex, hypothalamic and thalamic regions at P21. Cerebral blood volume measured with [14C]sucrose over a 2-min period was significantly increased over control levels in hypothalamus and cerebellum at P10 and in all brain regions, except hippocampus and brainstem, at P21. The widespread increase in BBB permeability is at least partly related to the blood pressure increase, 55 and 22% over control values at P10 and P21, respectively. In the P10 rat, generalized BBB leakage appears to be correlated to the widespread increase in cerebral metabolic and blood flow rates that we recorded previously in the same experimental conditions. Conversely, at P21, as previously shown in adults, there is a mismatch between the nature of the structures with increased BBB permeability and the regional distribution of cerebral blood flow and metabolism changes induced by PTZ seizures.
Aminoisobutyric Acids↗
Stereodifferentiation of 3-hydroxyisobutyric- and 3-aminoisobutyric acid in human urine by enantioselective multidimensional capillary gas chromatography-mass spectrometry.
The chiral metabolites 3-hydroxyisobutyric acid (HIBA) and 3-aminoisobutyric acid (AIBA) are intermediates in the pathways of L-valine and thymine and play an important role in the diagnosis of the very rare inherited metabolic diseases 3-hydroxyisobutyric aciduria (McKusick 236975) and methylmalonic semialdehyde dehydrogenase deficiency (McKusick 603178-MSDD). Until now only a few approaches have been made in enantioselective analysis of HIBA and AIBA and for that reason very little information is available on enantiomeric ratios of these metabolites in man. This paper reports on the simultaneous stereodifferentiation of HIBA and AIBA in human urine as corresponding N(O)-methoxycarbonyl methyl esters by derivatization with methyl chloroformate (MCF) using enantioselective multidimensional gas chromatography-mass spectrometry (enantio-MDGC/MS) with heptakis-(2, 3-di-O-methyl-6-O-tert.-butyl-dimethylsilyl)-beta-cyclodextrin as the chiral stationary phase. During this investigation urine samples from different patients and healthy controls were analyzed in order to reveal characteristic enantiomeric patterns of these metabolites. A trend of dominating R-HIBA excretion in the control urine samples investigated was observed. An excretion of more than 80% S-HIBA was found in the urines of two patients with ketonemic vomiting. There are some clues indicating a possible renal reabsorbtion of S-HIBA similar to those of S-AIBA. Furthermore, there was a significant finding with regard to the enantiomeric distribution of AIBA in a patient with MSDD - a markedly increased excretion of the S-enantiomer in contrast to the other samples. Using the enantiomeric ratios of AIBA, a previously investigated case of benign methylmalonic aciduria (bMMA) could be excluded from the diagnosis of MSDD.
Aldehyde Oxidoreductases↗