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At least 433 records · Page 24Linked to original sources
PubMed1995

Metabolism of cyclohexane carboxylic acid by the photosynthetic bacterium Rhodopseudomonas palustris.

Cyclohexane carboxylate supported relatively rapid growth (doubling times 7-8 h) of Rhodopseudomonas palustris under oxic or photosynthetic conditions, but did not serve as a substrate for either of the known aromatic CoA ligases. A CoA ligase that thioesterifies cyclohexane carboxylate was partially purified and did not cross react immunologically with the two CoA ligases purified previously from this bacterium. Crude extracts of R. palustris cells grown with a range of aromatic or alicyclic acids contained a dehydrogenase that reacted with cyclohexane carboxyl-CoA or cyclohex-1-ene carboxyl-CoA, using 2,6-dichlorophenolindophenol or ferricenium ion as electron carrier. This activity was not detected in extracts of adipate-, glutamate-, or succinate-grown cells. No oxidation or reduction of nonesterified cyclohexane carboxylate or cyclohexene carbocylate was detected in extracts of cells grown with aromatic or aliphatic substrates, neither aerobically nor anaerobically. A constitutively expressed thioesterase that hydrolyzed cyclohexane carboxyl-CoA and also some alicyclic and aliphatic CoA derivatives was purified and characterized. The enzyme had little or no activity on benzoyl-CoA or 4-hydroxybenzoyl-CoA. The presence of a thioesterase that effectively hydrolyzes cyclohexane carboxyl-CoA suggests that transient production of cyclohexane carboxylate is a physiological response to temporary excess of reductant during metabolism of aromatic compounds.

Amino Acid Sequence↗
PubMed2006

PEPT1 enhances the uptake of gabapentin via trans-stimulation of b0,+ exchange.

PURPOSE: The aims of this study were (1) to determine whether amino acid and dipeptide loading can improve the effective permeability of gabapentin and (2) to characterize the underlying mechanism that is responsible for this interaction. MATERIALS AND METHODS: An in situ single-pass rat intestinal perfusion model was used to assess the effective permeability of gabapentin in rat, in the absence and presence of cellular loading by amino acid and dipeptide mixtures. RESULTS: Compared to gabapentin alone, cellular loading with amino acid and dipeptide mixtures significantly improved the effective permeability of gabapentin by 46-79% in jejunum and by 67-72% in ileum (p < or = 0.01). However, coperfusion of glycylsarcosine (i.e., PEPT1 substrate), methionine sulfoximine (i.e., glutamine synthase inhibitor), or lysine and arginine (i.e., b(0,+) substrates) with the amino acid and dipeptide mixtures compromised the intestinal uptake of gabapentin. CONCLUSIONS: These findings demonstrate, for the first time, a direct relationship between the PEPT1-mediated uptake of a dipeptide and the trans-stimulated uptake of gabapentin (an amino acid-like drug) through the transport system b(0,+).

Amines↗
PubMed1985

Purification and characterization of an abscisic acid-inducible anionic peroxidase associated with suberization in potato (Solanum tuberosum).

An anionic peroxidase (EC 1.11.1.7), thought to be involved in suberization, was purified 110-fold from wound-healing slices of Solanum tuberosum by a combination of ammonium sulfate fractionation, Sephadex G-100 gel filtration, isoelectric focusing, and phenyl-Sepharose CL-4B chromatography in 24% yield. The purified enzyme was homogeneous as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and horizontal thin-layer polyacrylamide gel electrophoresis. The molecular weight of the enzyme was estimated to be 47,000 by both Sephadex G-100 gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This peroxidase was found to be a glycoprotein containing about 17% carbohydrate, approximately one-quarter of which was shown to be glucosamine residues. It was found to have an isoelectric point of 3.15. An anionic peroxidase was also isolated from abscisic acid-treated callus tissue culture of S. tuberosum by the above purification procedure. The two enzymes were shown to be immunologically similar, if not identical, based on their cross-reactivity with rabbit antibody prepared against the peroxidase from wound-healing slices, whereas the major cationic peroxidase from wound-healing slices did not cross-react with this antibody. The anionic enzyme from both sources showed very similar specific activities when assayed with a range of substrates, whereas the specific activities found for the cationic isozyme isolated from wound-healing slices were quite different.

Abscisic Acid↗
PubMed1987

Identification of an intermediate of delta-aminolevulinate biosynthesis in Chlamydomonas by high-performance liquid chromatography.

The first committed intermediate of the chlorophyll biosynthetic pathway is delta-aminolevulinic acid (ALA). In plant cells, ALA is formed from glutamate by a pathway not yet clearly defined. One of the proposed pathways involves the reduction of glutamate to glutamate-1-semialdehyde (GSA) via a glutamyl-tRNA intermediate. GSA is then converted to ALA by an aminotransferase. We are studying this pathway using partially purified components from Chlamydomonas reinhardtii in in vitro reactions with [3H]L-glutamate as the substrate and analysis of the radioactive reaction products via HPLC. In reactions either lacking GSA-aminotransferase or containing gabaculine (an inhibitor of aminotransferase), a radioactive intermediate is formed which cochromatographs with synthetic GSA. As observed previously for ALA synthesis, the synthesis of this intermediate has an absolute requirement for RNA, ATP, and active enzymes, while the requirement for NADPH is less stringent. Both the accumulated intermediate and the synthetic GSA can be converted to ALA by the aminotransferase without any additional substrates or cofactors. These results support previous observations that GSA or a very similar compound is an intermediate of ALA synthesis.

Aminolevulinic Acid↗
PubMed1983

Pharmacological manipulation of GABA system does not protect the goldfish optic tectum from the neuroexcitatory and neurotoxic action of kainic acid.

Inhibition of GABA transaminase which led to a several-fold increase of GABA levels in the goldfish optic tectum or diazepam pre-treatment, were unable to protect tectal neurons from kainic acid neurotoxicity, as judged by light and electron microscopic observations and by the drop of marker enzymes for neurotransmitters. In an in vitro preparation of tectal slices GABA, added to the incubation medium, had no effect on a metabolic parameter (CO2 production from exogenous glucose) related to the excitatory action of kainic acid. It is concluded that, in the goldfish optic tectum, pharmacological manipulation cannot enhance the activity of GABAergic circuits to the extent necessary to block the neuroexcitatory and neurotoxic action of kainic acid.

4-Aminobutyrate Transaminase↗
PubMed1980

Sensitivity of progesterone receptors to aurintricarboxylic acid. Inhibition of nuclear uptake, ATP and DNA binding.

When hen oviduct cytosol samples containing progesterone receptor complexed to [3H]progesterone were incubated with isolated nuclei in presence of 0.2 mM aurintricarboxylic acid, more than 50% inhibition occurred in the uptake of progesterone receptor by the nuclei. The activated form of progesterone receptor appeared to be more sensitive to the presence of aurintricarboxylic acid since pretreatment of non-activated progesterone receptor with the inhibitor and the subsequent removal of the latter prior to activation did not result in the inhibition of receptor uptake by the nuclei. Also, the binding of progesterone receptor to columns of DNA-cellulose of ATP-Sepharose was abolished under similar conditions. When nuclei, ATP-Sepharose or DNA-cellulose were preincubated with the inhibitor prior to the addition of receptor preparations, no such inhibition resulted indicating that the inhibitor may be interacting with the receptor protein and not complexing to ATP, DNA or sites in the nuclei. The steroid binding properties of progesterone receptor, however, remained intact under these conditions. Both A and B forms of progesterone receptor are equally sensitive to aurintricarboxylic acid presence when tested for their nuclear uptake. Aurintricarboxylic acid was also found to be very effective at low concentrations (0.25 mM) in eluting the receptor complexes off ATP-Sepharose columns without disrupting the steroid binding properties of progesterone receptor. Our results suggest that aurintricarboxylic acid is an effective inhibitor of progesterone receptor and that it may be acting by interfering with a site(s) on progesterone receptor which may be exposed upon activation and are involved in such processes as ATP binding, nuclear uptake and DNA binding. These observations suggest that use of aurintricarboxylic acid as a chemical probe for the analysis of progesterone receptor.

Adenosine Triphosphate↗
PubMed1986

Autoradiographic study of the distribution of [3H]gamma-aminobutyrate-accumulating neural elements in guinea-pig intestine: evidence for a transmitter function of gamma-aminobutyrate.

High affinity uptake, and the distribution of 3H-radiolabelled gamma-aminobutyrate (GABA), cis-3-aminocyclohexanecarboxylic acid, beta-alanine, proline, and leucine have been examined autoradiographically in laminar preparations of the myenteric plexus from the guinea-pig intestine. Following labelling with [3H]proline and [3H]leucine, which are incorporated into neurons, silver grains were concentrated over recognisable perikarya in the ganglia and meshworks of the plexus, whilst [3H]GABA labelled a smaller proportion of neurons and their processes. Specificity of labelling in the sites of [3H]GABA-uptake was established using combinations of labelled and unlabelled GABA, beta-alanine, and cis-3-aminocyclohexanecarboxylic acid, substrates for glial or neuronal high affinity GABA uptake systems. Only myenteric neurons and their processes were labelled significantly by [3H]GABA and its analogue cis-3-[3H]aminocyclohexanecarboxylic acid. Using autoradiographs of laminar preparations and paraffin sections, [3H]GABA labelling was found over nerve fibre bundles that could be traced from their ganglionic origins through the interconnecting meshworks of the myenteric plexus into the innervation of the deep muscular plexus of the circular muscle layer where GABA is evidently concerned with prejunctional modulation of transmitter release. The extensive but selective distribution of [3H]GABA high affinity uptake sites in neural elements of the guinea-pig myenteric plexus is consistent with GABA being an enteric neurotransmitter.

Alanine↗
PubMed1996

Determination of gabapentin in plasma by high-performance liquid chromatography.

A rapid and simple method for determination of the novel antiepileptic compound gabapentin [1-(aminomethyl)cyclohexaneacetic acid] in plasma is described. Blank human plasma was spiked with gabapentin (1.0-10.0 micrograms/ml) and internal standard [1-(aminomethyl)-cycloheptaneacetic acid; 5.0 micrograms/ml]. Individual samples were treated with 2 M perchloric acid, centrifuged and then derivatised with o-phthalaldehyde-3-mercaptopropionic acid. Separation was achieved on a Beckman Ultrasphere 5 microns reversed-phase column with mobile phase consisting of 0.33 M acetate buffer (pH 3.7; containing 100 mg/l EDTA)-methanol-acetonitrile (40:30:30, v/v). Eluents were monitored by fluorescence spectroscopy with excitation and emission wavelengths of 330 and 440 nm, respectively. The calibration curve for gabapentin in plasma was linear (r = 0.9997) over the concentration range 1.0-10.0 micrograms/ml. Recovery was seen to be > or = 90%. The inter- and intra-assay variations for three different gabapentin concentrations were < or = 10% throughout. The lower limit of quantitation was found to be 0.5 microgram/ml. Chromatography was unaffected by a range of commonly employed antiepileptic drugs or selected amino acids.

Acetates↗