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At least 523 records · Page 29Linked to original sources

PubMed1996

Feasibility of labeled alpha-acetamido-aminoisobutyric acid as new tracer compound for kinetic labeling of neutral amino acid transport: preparation of alpha-(N-[1-11C]acetyl)- and alpha-(N-[1-14C]acetyl)-aminoisobutyric acid.

The nonphysiological, nonracemic, branched-chain alpha-acetamido-aminoisobutyric acid was labeled with the carbon isotope 11C with the intention to use it in conjunction with positron emission tomography (PET) to measure the kinetics of amino acid transport in vivo. It was produced by the reaction of the novel 11C-precursor N-[1-11C]acetylpyridinium chloride with alpha-aminoisobutyric acid. Typically, 2 GBq of alpha-(N-[1-11C]acetyl)-aminoisobutyric acid were isolated with a specific activity of 12 to 20 GBq. mumol-1 at the time of application, and with a radiochemical purity of > 98%. The chemical identity of alpha-(N-[1-11C]acetyl)-aminoisobutyric acid was confirmed by comparison with alpha-(N-[1-14C]acetyl)-aminoisobutyric acid that was independently prepared by a standard acetylation procedure of alpha-aminoisobutyric acid using [1-14C]acetic anhydride. In vivo, both labeled substrates were not metabolized. In cell-culture experiments, 84% of the substrate entered the cells by the sodium-dependent amino acid transport system A, whereas 16% was taken up by the sodium-independent system. The uptake of the radiotracer was measured 20 min and 40 min postinjection in tumor-bearing male Copenhagen rats for assessment of its in vivo biodistribution.

Adenocarcinoma↗

PubMed1996

Formation of varanic acid, 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acid from 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid in Bombina orientalis.

Varanic acid (3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acid; 24-OH-THCA) is almost the sole component of bile acids in the bile of Bombina orientalis. To examine in the mechanism of the formation of 24-OH-THCA, radiolabeled (25R)- and (25S)-3 alpha, 7 alpha, 12 alpha-trihdroxy-5 beta-cholestanoic acids [(25R)- and (25S)-THCA] and (24E)-3 alpha, 7 alpha, 12 alpha-trihdroxy-5 beta-cholest-24-enoic acid (delta 24-THCA) were administered intraperitoneally to B. orientalis, gallbladder bile was collected after 24 h, and bile acids were subsequently extracted. Then the bile acids were analyzed by means of radio thin-layer chromatography and radio high-performance liquid chromatography after conversion to p-bromophenacyl ester derivatives. Although delta 24-THCA was not converted to 24-OH-THCA, (25R)-THCA and (25S)-THCA were transformed to (24R,25R)-24-OH-THCA and (24R,25S)-24-OH-THCA, respectively. These results strongly suggest that 24-OH-THCA was transformed via direct hydroxylation of the saturated side chain of THCA, not via hydration to an alpha, beta-unsaturated acid, delta 24-THCA, in B. orientalis.

Animals↗

PubMed1998

The hepato-renal syndrome: renal amino acid transport in bile duct ligated rats (DL)--influence of treatment with triiodothyronine or dexamethasone on renal amino acid handling in amino acid loaded rats.

The influence of triiodothyronine or dexamethasone on renal amino acid handling was investigated in anaesthetized, bile duct-ligated (DL) adult female rats. 3 days after DL, glomerular filtration rate (GFR) was unchanged whereas urine flow was decreased. Plasma concentrations of 5 out of 16 amino acids were significantly enhanced after DL. On the other hand, the fractional excretion (FE) of 11 out of 16 amino acids was significantly reduced as a sign of improved reabsorption capacity. Bolus injections of leucine (20 mg/100 g b.wt.), glutamine (45 mg/100 g b.wt.), or taurine (45 mg/100 g b.wt.) were followed by a temporary increase in the FE of the administered amino acids as well of the endogenous amino acids which were not administered. This phenomenon was more pronounced in DL than in control rats. Under load conditions, dexamethasone (60 microg/100 g b.wt.) or triiodothyronine (20 microg/100 g b.wt.) treatment for 3 days, i.p. once daily, was followed by a stimulation of renal amino acid reabsorption in DL rats. The increase in fractional amino acid excretion after amino acid load was significantly lower than in untreated rats. This effect was also more pronounced in DL rats.

Amino Acids↗

PubMed2004

Hydrophilic and hydrophobic sorption of organic acids by variable charge soils: effect of chemical acidity and acidic functional group.

Sorption of organic acids by variable-charge soil occurs through both hydrophilic and hydrophobic sorption. In this study, the effect of chemical acidity and the type of acidic functional group on the relative contribution of hydrophilic and hydrophobic processes to sorption by a gibbsite-dominated and a kaolinite-dominated variable-charge soils was quantified by measuring sorption isotherms from different electrolytes (CaCl2, Ca(H2PO4)2, and KCl). The A1 soil is dominated by gibbsite whereas the DRC soil is primarily kaolinite. The organic acids investigated include five chlorinated phenols (pentachlorophenol, 2,3,4,6-tetrachlorophenol, 2,4,6-trichlorophenol, 2,4,5-trichlorophenol, and 2,4-dichlorophenol) with pKa values ranging from 4.69 to 7.85 and two acidic herbicides (2,4-D (pKa = 2.8) and prosulfuron (pKa = 3.76)) that contain carboxyl and urea functional groups, respectively. Anion exchange of chlorinated phenols and prosulfuron on both variable-charge soils as well as 2,4-D sorption on the A1 soil was linearly correlated to chemical acidity. The effective positive surface charge [AEC/(AEC + CEC)] and the anionic fraction of the organic acid in solution, which are both pH-dependent, were sufficient to estimate the contribution of anion exchange to organic acid sorption except for 2,4-D sorption by DRC soil. The latter was much greater than would be predicted from the pKa of 2,4-D. Calcium bridging between silanol edge group and 2,4-D was hypothesized and corroborated by differences in sorption measured from KCl and CaCl2 solutions. For predicting contributions from hydrophobic processes, a log-log linear relationship between pH-dependent octanol-water (Kow(pH)) and organic carbon-normalized sorption coefficients (Koc(pH)) appeared adequate.

2,4-Dichlorophenoxyacetic Acid↗

PubMed1996

Studies on acid oils and fatty acids for chickens. I. Influence of age, rate of inclusion and degree of saturation on fat digestibility and metabolisable energy of acid oils.

1. Using a multi-rate assay, 3 commercial acid oils (sunflower, soyabean and tallow) were evaluated for AMEn and added fat digestibility with broiler chicks, at 11, 25, 39, 53 and 60 d of age. The regression equations of AMEn values or ME of available fat on rate of inclusion of fat were calculated. 2. Significance was achieved for linear regression but not for quadratic regression in both variables; neither rate of inclusion nor age of birds (except for tallow acid oil at 25 d) significantly affected the AMEn or ME of fat. Metabolisable energy of fat (on a dry matter basis) calculated from combined linear regression equations was 19.14MJ/kg for sunflower acid oil, 18.09MJ/kg for tallow acid oil and 27.94MJ/kg for soyabean acid oil. Differences between sunflower and soyabean acid oils were attributed in variations in unsaponifiable and non-eluted materials of both fats. 3. Abdominal fat pad weight and its relationship to carcase weight were also studied with birds slaughtered at 67 d of age. Chicks given tallow acid oil deposited larger amounts of abdominal fat, and this deposition was directly related to the rate of inclusion of acid oil in the diet.

Abdomen↗

PubMed1996

Acid tolerance in Listeria monocytogenes: the adaptive acid tolerance response (ATR) and growth-phase-dependent acid resistance.

Listeria monocytogenes acquired increased acid tolerance during exponential growth upon exposure to sublethal acid stress, a response designated the acid tolerance response (ATR). Maximal acid resistance was seen when the organism was exposed to pH 5.0 for 1 h prior to challenge at pH 3.0, although intermediate levels of protection were afforded by exposure to pH values ranging from 4.0 to 6.0. A 60 min adaptive period was required for the development of maximal acid tolerance; during this period the level of acid tolerance increased gradually. Full expression of the ATR required de novo protein synthesis; chloramphenicol, a protein synthesis inhibitor, prevented full induction of acid tolerance. Analysis of protein expression during the adaptive period by two-dimensional gel electrophoresis revealed a change in the expression of at least 23 proteins compared to the non-adapted culture. Eleven proteins showed induced expression while 12 were repressed, implying that the ATR is a complex response involving a modulation in the expression of a large number of genes. In addition to the exponential phase ATR, L.monocytogenes also developed increased acid resistance upon entry into the stationary phase; this response appeared to be independent of the pH-dependent ATR seen during exponential growth.

Adaptation, Physiological↗

PubMed1975

[Investigations on the utilisation of parenterally administered amino acids by premature and small-for-dates neonates. II. Investigations of elimination half life time, elimination constants, transfer and clearances of amino acids after short-time infusion of L-amino acid mixtures (author's transl)].

10 ml/kg body weight of a 5% standardized L-amino-acid-mixture was given within the first 25 days to 25 prematurely born infants of 32--37 weeks gestationale and 5 small-for-dates newborns. We studied the metabolic kinetics of these amino acids in the serum and calculated elimination half life time, elimination constants, clearance and transfer rates of the single amino acids. The results were correlated with sex, nutritional state and age. 5 additional experiments were performed with 3 prematurely born infants and 2 small-for-dates newborns. The following results were of special interests: 1. Nearly all amino-acids had half life times between 30 and 50 min. Ornithine and tryptophane were more (half life time: 70 and about 50 min, respectively) slowly eliminated, while arginine and glutamic acid had half life times of between 5 and 15 min. 2. There was no statistically significant differences between sexes. 3. Eutrophic prematures eliminated the amino acids much faster then the hypotrophic ones. 4. Hypotrophic premature infants showed slow elimination of nearly all amino acids compared with hypotrophic newborns. 5. The elimination of nearly all amino acids studied grew faster with increasing age. The most significant differences were registered between the 1st and 3rd weeks of life.

Age Factors↗

PubMed1993

The CoA esters of 2-methyl-branched chain fatty acids and of the bile acid intermediates di- and trihydroxycoprostanic acids are oxidized by one single peroxisomal branched chain acyl-CoA oxidase in human liver and kidney.

Rat liver peroxisomes contain three acyl-CoA oxidases: palmitoyl-CoA oxidase, which oxidizes the CoA esters of straight chain fatty acids and prostaglandins; pristanoyl-CoA oxidase, which oxidizes the CoA esters of 2-methyl-branched fatty acids (e.g. pristanic acid); and trihydroxycoprostanoyl-CoA oxidase, which oxidizes the CoA esters of the bile acid intermediates di- and trihydroxycoprostanic acids (Van Veldhoven, P. P., Vanhove, G., Asselberghs, S., Eyssen, H. J., and Mannaerts, G. P. (1992) J. Biol. Chem. 267, 20065-20074). In the present report we demonstrate that human liver peroxisomes contain only two acyl-CoA oxidases: palmitoyl-CoA oxidase, which oxidizes the CoA esters of straight chain fatty acids and prostaglandins, and a novel branched chain acyl-CoA oxidase, which oxidizes the CoA esters of 2-methyl-branched fatty acids as well as those of the bile acid intermediates (which also possess a 2-methyl substitution in their side chains). The branched chain acyl-CoA oxidase was purified to near homogeneity by means of column chromatography. It appeared to be a 70-kDa monomeric protein that did not cross-react with antisera raised against rat palmitoyl-CoA oxidase and pristanoyl-CoA oxidase. No indication was found for the presence of a separate trihydroxycoprostanoyl-CoA oxidase in human liver. The branched chain acyl-CoA oxidase was present also in human kidney, suggesting that it is expressed in other extrahepatic tissues as well. Our results explain a number of clinical-chemical observations made in certain cases of peroxisomal beta-oxidation disorders.

Acyl Coenzyme A↗

PubMed1964