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At least 721 records · Page 40Linked to original sources
PubMed1989

Brown adipose tissue (Na+-K+)-ATPase activity and substrate uptake during the breeding cycle of rats.

Brown adipose tissue (Na+-K+)-ATPase activity, in vitro glucose and 2-aminoisobutyric acid uptake, as well as mitochondrial GDP-binding and succinate dehydrogenase activity were determined in order to study the relationship between these parameters and the thermogenic status. Analysis were carried out on control animal, pregnant rats, dams and pups during lactation, GDP-binding, (Na+-K+)-ATPase and glucose uptake were found to be decreased in brown adipose tissue from pregnant rats and dams, and increased in pups, 2-aminoisobutyric acid uptake was only increased in pups, but no changes were observed in the other experimental groups tested. GDP-binding and (Na+-K+)-ATPase activity showed a parallelism which suggests that the enzyme is a good index of thermogenic status of the animal.

Adipose Tissue, Brown↗
PubMed1983

Intrauterine growth retardation and diabetic pregnancy: two types of fetal malnutrition.

Placental transfer of alpha-aminoisobutyric acid and methylglucose was studied near term in normal guinea pigs carrying growth-retarded fetuses and in streptozotocin-treated diabetic guinea pigs. Compared with their normal littermates, growth-retarded fetuses had lower placental weights and a diminished transfer of both nutrient analogues in proportion to the reduction in fetal weight. Fetuses from diabetic animals had normal fetal weight and placental methylglucose transfer but reduced litter size and a 40% reduction in placental alpha-aminoisobutyric acid transfer. These data suggest that intrauterine growth retardation in an otherwise normal pregnancy is associated with a small placenta and a reduced transfer of nutrients. Diabetic pregnancy may represent a different type of fetal malnutrition due to amino acid deprivation. It is speculated that birth weight does not necessarily reflect the degree of fetal malnutrition in diabetic pregnancy since fetal growth may be maintained by glucose and fat deposition.

3-O-Methylglucose↗
PubMed1987

Effect of triiodothyronine on system A amino acid transport in cells of rat submandibular gland.

The effect of L-3,5,3'-triiodothyronine (T3) on alpha-aminoisobutyric acid (AIB) transport in isolated cell suspensions of rat submandibular gland was investigated. The uptake of ATB by these cells appeared to require extracellular Na+ and was inhibited by ouabain (10(-3) M). Cell suspensions from thyroidectomized rats which have been given three successive doses of T3 on alternate days (50 micrograms/100 g BW) showed a significant increase in AIB uptake compared with cells isolated from thyroidectomized rats treated with diluent. Efflux of AIB from the cell suspension was not affected by T3. There was no significant changes in AIB uptake 12 h after a single injection of T3 (50 micrograms/100 g BW). However, there was a significant 49% and 65% increase in AIB net uptake at 24 and 48 h, respectively, after T3 treatment. Under similar conditions, the cell suspension showed a 48% increase in NaK-ATPase activity at 12 h and to a peak of 61% at 24 h. Therefore, changes in NaK-ATPase activity preceded the changes in AIB net uptake upon treatment with T3, implying that AIB uptake is probably mediated, at least in part, by the activity of NaK-ATPase.

Amino Acids↗
PubMed1992

Effect of inorganic mercury on in vitro placental nutrient transfer and oxygen consumption.

The effect of mercury (HgCl2) on placental amino acid and glucose transfer as determined by the use of their nonmetabolizable radioactive analogues, aminoisobutyric acid (AIB) and 3-o-methyl glucose (3MG), respectively, was studied in an in vitro perfusion model of a term human placenta. Hg2+ was found to decrease the transfer and accumulation of AIB without affecting 3MG transfer. It was also found to decrease the placental oxygen consumption rate. Placental circulation and tissue morphology remained intact, as demonstrated by the antipyrine transfer rate, and by electron microscopy, respectively. The mechanism by which Hg2+ may interfere with placental amino acid transfer and accumulation is discussed. Although much higher concentrations than those found in the ordinary polluted environment were used, this is the first report showing that Hg2+ interferes with an essential human placental function in a system employing a whole human placental cotyledon. This finding may indicate the possible involvement of Hg2+ in impaired organogenesis in early pregnancy or deranged fetal growth during the last trimester.

3-O-Methylglucose↗
PubMed2000

The NMR solution structure of the ion channel peptaibol chrysospermin C bound to dodecylphosphocholine micelles.

Chrysospermin C is a 19-residue peptaibol capable of forming transmembrane ion channels in phospholipid bilayers. The conformation of chrysospermin C bound to dodecylphosphocholine micelles has been solved using heteronuclear NMR spectroscopy. Selective 15N-labeling and 13C-labeling of specific alpha-aminoisobutyric acid residues was used to obtain complete stereospecific assignments for all eight alpha-aminoisobutyric acid residues. Structures were calculated using 339 distance constraints and 40 angle constraints obtained from NMR data. The NMR structures superimpose with mean global rmsd values to the mean structure of 0. 27 A (backbone heavy atoms) and 0.42 A (all heavy atoms). Chrysospermin C bound to decylphosphocholine micelles displays two well-defined helices at the N-terminus (residues Phe1-Aib9) and C-terminus (Aib13-Trp-ol19). A slight bend preceding Pro14, i.e. encompassing residues 10-12, results in an angle of approximately 38 degrees between the mean axes of the two helical regions. The bend structure observed for chrysospermin C is compatible with the sequences of all 18 long peptaibols and may represent a common 'active' conformation. The structure of chrysospermin C shows clear hydrophobic and hydrophilic surfaces which would be appropriate for the formation of oligomeric ion channels.

Amino Acid Sequence↗
PubMed1978

Sodium-dependent amino acid transport by cultured hamster cells: membrane vesicles retain transport changes due to glucose starvation and cycloheximide.

Enhanced alpha-aminoisobutyric acid transport by hamster cells cultured in the absence of D-glucose has been demonstrated in isolated membrane vesicles. The observed enhancement was seen in the presence but not in the absence of Na+. Kinetic analysis of transport using both the intact cells and the membrane vesicles showed that the overall enhancement was associated with an increase in Vmax. Decreases in transport activity by intact cells resulting from extended exposure of the cells to inhibitors of protein synthesis, such as cycloheximide, were also evident in membrane vesicles. The use of metabolically inactive membrane vesicles demonstrated that amino acid uptake by intact cells is a transport property of the plasma membrane. In addition, this study shows that membrane vesicle preparations can be exploited for the purpose of studying the regulation of amino acid transport. Taken together, the data suggest that carrier turnover is involved in the regulation of amino acid transport in animal cells.

Amino Acids↗
PubMed1974

Regulation of amino acid transport in kidney cortex of newborn rats.

After incubation at 37 degrees C the subsequent uptake of alpha-aminoisobutyric acid, cycloleucine, glycine, and L-proline by newborn (as compared to adult) rat kidney cortex slices is enhanced. The effect is abolished by the presence of cycloheximide, actinomycin D, and high concentrations of the above-mentioned amino acids in the medium during the 37 degrees C incubation prior to measurement of uptake. The data suggest that there is an adaptive control mechanism which is expressed on incubation at 37 degrees C and which can regulate amino acid transport in newborn rat kidney cortex.

Amino Acids↗
PubMed1978

Placental amino acid uptake. IV. Transport microvillous membrane vesicles.

The recent characterization of a vesicular microvillous plasma membrane preparation from human placenta has made possible study of the characteristics of amino acid transport by the isolated membrane. Variation of medium osmolality demonstrated that alpha-aminoisobutyric acid (AIB) is taken up virtually entirely into a vesicular space. Vesicular volume was determined from equilibrium uptake of three dissimilar nonamino acid substrates, all of which gave a common value. Temperature dependence, saturability, specificity, and similarity of kinetic constants all indicated that AIB uptake by the vesicles resembles that by whole villous tissue. AIB uptake was stimulated specifically by an inward sodium gradient and unaffected by an outward potassium gradient. The persistence of stimulation up to 2 h after the gradient was established could be correlated with the slow equilibration of sodium across the membrane. AIB exodus could be studied with minimal problems of substrate recapture by using preloaded membrane vesicles bound tightly to cellulose ester filters to facilitate transfer to fresh medium. The exodus process was saturable with a Km considerably greater than that for entry.

Alkaline Phosphatase↗
PubMed1986

The effect of prostaglandin E2 (PGE2) on amino acid uptake and protein formation by lung fibroblasts.

The effect of prostaglandin E2 (PGE2) on the utilization of extracellular amino acids by fetal lung fibroblasts was examined. PGE2 decreased the uptake of proline and aminoisobutyric acid (AIB) by quiescent fibroblasts in culture. The uptake of AIB by serum-activated cultures was also dramatically decreased by PGE2. The PGE2-induced decrease in the uptake of AIB was first observed at 4 h following the addition of the effector molecule to the cultures. PGE2 did not affect the uptake of leucine. The addition of cycloheximide also resulted in a decrease in the uptake of proline, similar to that induced by PGE2 at 5 X 10(-8) M. The combination of cycloheximide and PGE2 resulted in a further decrease in proline uptake. Kinetic analysis of AIB uptake following a 24-h PGE2 treatment showed an increase in the apparent Km as compared with untreated cultures. The prostaglandin remained active for at least 72 h after the addition of the molecule. Removal of the PGE2 was followed by an influx of proline into the cells. The decrease in proline uptake was associated with a decrease in the amount of intracellular free proline and an overall decrease in the amount of cell-associated protein. While PGE2 is known to increase intracellular protein degradation, the effect of PGE2 on amino acid uptake was not the result of an increase in the intracellular concentration of amino acids (transinhibition).

Amino Acids↗
PubMed1989

Metabolic effects induced by epidermal growth factor (EGF) in cells expressing EGF receptor mutants.

The epidermal growth factor (EGF) receptor tyrosine kinase activity is required for both the earliest EGF-stimulated post-binding events (enhancement of inositol phosphate formation and Ca2+ influx, activation of Na+/H+ exchange), and the ultimate EGF-induced mitogenic response. To assess the role of EGF receptor kinase in EGF-induced metabolic effects (2-deoxyglucose and 2-aminoisobutyric acid uptake), we used NIH3T3 cells (clone 2.2), which do not possess endogenous EGF receptors and which were transfected with cDNA constructs encoding either wild type or kinase-deficient human EGF receptor (HER). In addition, we tested the importance of three HER autophosphorylation sites (Tyr-1068, Tyr-1148, and Tyr-1173) in transduction of EGF-stimulated 2-deoxyglucose uptake. Taking our data together, we conclude the following: (i) HER tyrosine kinase activity is required to elicit EGF stimulation of both 2-deoxyglucose and 2-aminoisobutyric acid uptake; (ii) mutations on individual HER autophosphorylation sites, Tyr-1068, Tyr-1148, and Tyr-1173 do not impair EGF-stimulated 2-deoxyglucose uptake.

Aminoisobutyric Acids↗
PubMed1981

Sugar and amino acid transport from the rat uterine lumen: effects of estrogen and progesterone.

Sugar and amino acid transport and diffusion from the uterine lumen were evaluated in either castrated rats 4 or 24 h after iv injection of 17 beta-estradiol (0.1--10 microgram) or in estrogen-primed castrated rats 12 or 24 h after iv injection of progesterone (25--250 microgram). Uptake phenomena were evaluated by selectively exposing the uterine luminal surface to a Ringer's solution containing [U-14C]D-mannitol and [3H]3-O-methyl-D-glucose or [3H]alpha-aminoisobutyric acid for a 30-sec incubation. Diffusion (D-mannitol uptake) decreased significantly 4 h (but not 24 h) after estrogen and 12 and 24 h after progesterone treatment. [3H]3-O-methyl-D-glucose transport increased significantly both 4 h (120--380%) and 24 h (50--200%) after estrogen. Although [3H]3-O-methyl-D-glucose transport was not significantly changed from that in the vehicle-injected control 12 or 24 h after progesterone, comparison of the transport at 12 h (reduced) to that at 24 h (increased) revealed a significant difference in the responses to progesterone treatment at these two times. [3H]alpha-aminoisobutyric acid transport increased significantly 4 and 24 h after only a pharmacological dose of 17 beta-estradiol and was unchanged 24 h after progesterone administration. In summary, uterine luminal diffusion and transport phenomena are hormone sensitive, with estrogen exerting a more pronounced effect on transport than does progesterone. Thus, through modulation of luminal transport mechanisms, these hormones may regulate substrate levels and, hence, their availability to the developing conceptus during different reproductive states in the rat.

Aminoisobutyric Acids↗
PubMed1997

Multitracer studies during gene therapy of hepatoma cells with herpes simplex virus thymidine kinase and ganciclovir.

UNLABELLED: Using different tracers of tumor metabolism, the application of PET for monitoring gene therapy with the suicide gene herpes simplex virus thymidine kinase (HSVtk) is investigated in this in vitro study. METHODS: Morris hepatoma cells were transfected with a retroviral vector bearing the HSVtk gene, and different clones were established by selection with the neomycin analog G418. Thereafter, uptake measurements using fluorodeoxyglucose (FDG), 3-O-methylglucose, aminoisobutyric acid and methionine were performed in a thymidine kinase (TK)-expressing cell line and in control cells bearing the empty vector in the presence of different concentrations of ganciclovir (GCV). These experiments were done up to 48 hr after the onset of therapy. The values were expressed as Bq/well or as Bq/10(5) cells. RESULTS: During GCV treatment therapy, a decrease of the uptake/well was measured for all tracers in the TK-expressing cell line. After normalization to the viable cell number, the uptake for FDG and 3-O-methylglucose increases up to 195% after 24 hr incubation with GCV. A high-pressure liquid chromatography analysis revealed a decline of the FDG-6-phosphate fraction after 48 hr incubation with GCV. Consequently, a normalization of FDG uptake was observed after this incubation period, whereas the 3-O-methylglucose uptake was still increased. Experiments performed with different amounts of TK-expressing cells and control cells showed that these effects are dependent on the percentage of TK-expressing cells. The aminoisobutyric acid uptake decreases to 47%, while the methionine uptake decreases in the acid-insoluble fraction (to 17%) and increases in the acid-soluble fraction (to 150%). CONCLUSION: These data indicate that combinations of the PET tracers used in these experiments may be applied for monitoring gene therapy with HSVtk. The increase in FDG and 3-O-methylglucose uptake in vitro is interpreted as stress reaction of the tumor cells. However, an uncoupling of transport and phosphorylation was observed after 48 hr incubation. The amino acid uptake experiments point to an inhibition of protein synthesis as well as of the neutral amino acid transport.

3-O-Methylglucose↗
PubMed1982

A feasibility study in the development of biological markers for ovarian cancer.

As a primary feasibility study for the selection of biomarkers for more extended clinical evaluation, 17 potential biomarker candidates were measured in the body fluids of patients with ovarian carcinoma. For comparative purposes, patients were staged and separated into three groups: those considered completely free of disease, those with residual but minimal tumor, and those with advanced disease. Individual markers included plasma carcinoembryonic antigen, serum human chorionic gonadotrophin, urinary beta-aminoisobutyric acid, serum UDP-galactosyltransferase, and urinary hydroxyproline. Structurally related groups of biomarkers included six modified nucleosides and three polyamines analyzed in urine, and three serum protein-bound neutral carbohydrates. The respective chromatographic methods developed for these latter biochemical materials enabled all the individual compounds in each group to be quantitated simultaneously in one analytical run. The general frequency and degree of elevation for the total number of biomarkers was directly proportional to increasing tumor burden with specific exceptions, human chorionic gonadotropin and beta-aminoisobutyric acid. Galactosyltransferase was the most frequently elevated in the limited disease categories. Several of the biomarkers were elevated in the majority of patients with advanced disease and appeared potentially superior to carcinoembryonic antigen or human chorionic gonadotrophin.

Aminoisobutyric Acids↗
PubMed1991

Comparison of the effects of various amino acids on glycogen synthesis, lipogenesis and ketogenesis in isolated rat hepatocytes.

Several amino acids were found to stimulate glycogen synthesis and lipogenesis, and to inhibit ketogenesis in isolated rat hepatocytes. When hepatocytes were incubated in the presence of 20 mM-glucose, the amino acids could be classified in decreasing order of efficiency as follows: glutamine and proline, alanine, aminoisobutyric acid, asparagine and histidine for stimulation of glycogen synthesis; glutamine, proline and alanine for stimulation of lipogenesis; proline and glutamine for inhibition of ketogenesis. The study of the time course revealed that the rates were not linear and were preceded by a lag period. In all conditions studied, glutamine and proline were found to have similar quantitative effects on glycogen synthesis and lipid metabolism. However, their effects differ qualitatively. Indeed, the effects of proline on glycogen synthesis, lipogenesis and glutamate and aspartate content were faster. Moreover, proline increased the hydroxybutyrate/acetoacetate ratio, whereas glutamine did not change it. Incubation of hepatocytes with aminoisobutyric acid or under hypo-osmotic conditions, which increased cell volume and mimicked the amino acid-induced stimulation of glycogen synthesis, had little effect on lipogenesis. In hepatocytes incubated without glucose, ketogenesis was inhibited, in decreasing order of efficiency, by alanine, asparagine, glutamine and proline. Under these conditions, glutamine increased, alanine decreased and asparagine did not affect the concentration of malonyl-CoA. This indicates that the latter cannot be responsible for the inhibition of ketogenesis by alanine and asparagine.

Amino Acids↗
PubMed2001

Detection of beta-ureidopropionase deficiency with HPLC-electrospray tandem mass spectrometry and confirmation of the defect at the enzyme level.

The pyrimidine bases uracil and thymine are degraded via the consecutive action of three enzymes to beta-alanine and beta-aminoisobutyric acid, respectively. To date, a number of patients have been described with a deficiency of dihydropyrimidine dehydrogenase and dihydropyrimidinase, the first two enzymes of the pyrimidine degradation pathway. In this study, we demonstrate that the first patient presenting with N-carbamyl-beta-amino aciduria, due to a deficiency of beta-ureidopropionase, was easily diagnosed at the metabolite level using HPLC-tandem mass spectrometry. Urinary analysis showed strongly elevated levels of N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyric acid, with normal or moderately increased levels of the pyrimidine bases and the dihydropyrimidines, respectively. The deficiency of beta-ureidopropionase was confirmed by measuring all three enzymes of the pyrimidine degradation pathway. No activity of beta-ureidopropionase could be detected in a liver biopsy of the patient, while a normal activity of dihydropyrimidine dehydrogenase and dihydropyrimidinase was present. Thus, HPLC-tandem mass specrometry proved to be a powerful tool for the initial diagnosis of patients with deficiency of beta-ureidopropionase.

Amidohydrolases↗
PubMed2003

Disruption of the beta-sheet structure of a protected pentapeptide, related to the beta-amyloid sequence 17-21, induced by a single, helicogenic C(alpha)-tetrasubstituted alpha-amino acid.

Fifteen years ago it was shown that an alpha-aminoisobutyric acid (Aib) residue is significantly more effective than an L-Pro or a D-amino acid residue in inducing beta-sheet disruption in short model peptides. As this secondary structure element is known to play a crucial role in the neuropathology of Alzheimer's disease, it was decided to check the effect of Aib (and other selected, helix inducer, C(alpha)-tetrasubstituted alpha-amino acids) on the beta-sheet conformation adopted by a protected pentapeptide related to the sequence 17-21 of the beta-amyloid peptide. By use of FT-IR absorption and 1H NMR techniques it was found that the strong self-association characterizing the pentapeptide molecules in weakly polar organic solvents is completely abolished by replacing a single residue with Aib or one of its congeners.

Amino Acid Substitution↗
PubMed2001

Blood-brain barrier permeability during dopamine-induced hypertension in fetal sheep.

Dopamine is often used as a pressor agent in sick newborn infants, but an increase in arterial blood pressure could disrupt the blood-brain barrier (BBB), especially in the preterm newborn. Using time-dated pregnant sheep, we tested the hypothesis that dopamine-induced hypertension increases fetal BBB permeability and cerebral water content. Barrier permeability was assessed in nine brain regions, including cerebral cortex, caudate, thalamus, brain stem, cerebellum, and spinal cord, by intravenous injection of the small tracer molecule [(14)C]aminoisobutyric acid at 10 min after the start of dopamine or saline infusion. We studied 23 chronically catheterized fetal sheep at 0.6 (93 days, n = 10) and 0.9 (132 days, n = 13) gestation. Intravenous infusion of dopamine increased mean arterial pressure from 38 +/- 3 to 53 +/- 5 mmHg in 93-day fetuses and from 55 +/- 5 to 77 +/- 8 mmHg in 132-day fetuses without a decrease in arterial O(2) content. These 40% increases in arterial pressure are close to the maximum hypertension reported for physiological stresses at these ages in fetal sheep. No significant increases in the brain transfer coefficient of aminoisobutyric acid were detected in any brain region in dopamine-treated fetuses compared with saline controls at 0.6 or 0.9 gestation. There was also no significant increase in cortical water content with dopamine infusion at either age. We conclude that a 40% increase in mean arterial pressure during dopamine infusion in normoxic fetal sheep does not produce substantial BBB disruption or cerebral edema even as early as 0.6 gestation.

Aminoisobutyric Acids↗
PubMed1976

Colchicine-sensitive structures and lymphocyte activation.

The possible modulatory role of microtubules or closely related colchicine-sensitive structures in the response of human lymphocytes to mitogenic lectins was investigated. Colchicine (0.1 to 10 muM) AND VINBLASTINE (0.1 TO 10 MUM) inhibited early [14C]-aminoisobutyric acid and late [3H]-thymidine uptake in phytohemagglutinin-and concanavalin A-stimulated human lymphocytes but failed to alter 45Ca uptake. Lumicolchicine, an inactive congener of colchicine, was ineffective in all three systems. Both microtubular agents accentuated and prolonged the early cyclic AMP response to lectin. Little or no alteration in cyclic AMP levels was seen with colchicine or vinblastine alone or in combination with PGE (10MUM) or epinephrine (1muM) suggesting that the effect on cyclic AMP metabolism is largely selective for lectin stimulation. Neither microtunular agent altered 125I-concanacalin A binding. Since the inhibition of DNA synthesis was throughout the culture period and early aminoisobutyric acid uptake is affected, it appears that these agents are acting on an early event, or events, in the activation sequence. Although the mechanism of the inhibition is not known, the effect of colchicine and vinblastine in prolonging the cyclic AMP response to lectin may be involved. Alternatively, alterations in microtubules assembly may exert effects on membrane architecture interfering with propagation of the stimulus from the membrane to the cell interior.

Aminoisobutyric Acids↗