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T A Alston

Publications and source records attributed to T A Alston.

35 records · Page 2Linked to original sources
PubMed1986

Amino acid neurotransmitters in the CNS: properties of diaminobutyric acid transport.

Uptake of L-2,4-diaminobutyric acid (DABA), a positively charged analogue of gamma-aminobutyric acid (GABA), by a synaptosomal fraction isolated from rat brain occurred with a Km of 54 +/- 12 microM and a Vmax of 1.3 +/- 0.2 nmol/min/mg protein. The transport of DABA was inhibited competitively by GABA whereas that of GABA was affected in the same manner by addition of DABA. The maximal accumulation of DABA ([DABA]i/[DABA]c) was observed to increase as the second power of the transmembrane electrical potential ([K+]i/[K+]e) and the first power of the sodium ion concentration gradient. These findings indicate that DABA is transported on the GABA carrier with a net charge of +2, where one charge is provided by the cotransported Na+ and the second is contributed by the amino acid itself. Since uptake of GABA, an electroneutral molecule, is accompanied by transfer of two sodium ions, the results obtained with DABA suggest that one of the sodium binding sites on the GABA transporter is in proximity to the amino acid binding site.

Aminobutyrates↗
PubMed1985

Generation of nitric oxide by enzymatic oxidation of N-hydroxy-N-nitrosamines.

The nitric oxide (N = O) free radical exhibits potent cytocidal, mutagenic and vasodilatory properties. We have examined the hypothesis that the hydroxynitrosamino functionality (see sequence in text), which occurs naturally in antineoplastic and antihypertensive agents, will directly generate N = O following peroxidatic 1-electron oxidation. Cupferron (see sequence in text) is indeed an excellent (k greater than 10(7) m-1 s-1) substrate for horseradish peroxidase. The products are N = O and nitrosobenzene (phi - N = O) which are generated and consumed as follows. First, cupferron is oxidized by the classical peroxidatic mechanism to form an unstable nitroxide free radical (see sequence in text) which then forms N = O and phi - N = O spontaneously (see sequence in text). The N = O then reacts with phi - N = O to reform cupferron (see sequence in text) or with the enzyme to generate the characteristic peroxidase--N = O chromophore. Simultaneously, in a competitive reaction with O2, the N = O is converted to NO-2 (4N = O + O2 + 2H2O------------4NO-2 + 4H+). The reactivity of hydroxynitrosamino compounds with horseradish peroxidase is in the order cupferron greater than hydroxynitrosaminomethane greater than alanosine. These model reactions, involving direct oxidation of the hydroxynitrosamino moiety, comprise a novel pathway for the biological production of N = O.

Chemical Phenomena↗
PubMed1983

Suicide inactivation of D-amino acid oxidase by 1-chloro-1-nitroethane.

Given that the oxidation of nitroethane by D-amino acid oxidase proceeds through a transient carbinolamine adduct at the N5 position of the active-site FAD cofactor (Porter, D. J. T., Voet, J. G., and Bright, H. J. (1973) J. Biol. Chem. 248, 4400-4416), it follows that 1-chloro-1-nitroethane should generate a stable amide at N5 and thereby function as a suicide inactivator of this enzyme. This hypothesis was validated as follows. 1-Chloro-1-nitroethane, as the nitronate ion (pKa = 7.0), inactivated D-amino acid oxidase completely with a Km value of 2 mM and a maximum rate of 0.02 s-1. The chloro and nitro groups were quantitatively recovered as free Cl- and NO2(-) after the enzyme was inactivated by 1.5 flavin equivalents of 1-chloro-1-nitroethane. Inactivation did not require O2 and was accompanied by bleaching of the flavin under both anaerobic and aerobic conditions. The modified coenzyme of the inactivated enzyme was identified as N5-acetyl-1,5-dihydro FAD. The enzyme catalyzes the oxidation of 1-chloro-1-nitroethane to acetate approximately 0.5 times as rapidly as the enzyme catalyzes suicide inactivation. The transient intermediate which is common to both the inactivation and oxidation pathways must be N5-(1-X-1-hydroxyethyl)-1,5-dihydro FAD, where X = nitro or chloro.

Alanine↗
PubMed1977

3-Nitropropionate, the toxic substance of Indigofera, is a suicide inactivator of succinate dehydrogenase.

We have shown that 3-nitropropionate, an isoelectronic analogue of succinate, is a suicide inactivator of succinate dehydrogenase [succinate:(acceptor) oxidoreductase, EC 1.3.99.1] as follows. (i) When rat liver mitochondria oxidize succinate in the presence of 3-nitropropionate carbanion, the rate of O(2) consumption decreases exponentially to a zero value. This pattern is duplicated by subsequent additions of mitochondria. The dependence of the apparent first-order rate constant for enzyme inhibition, as well as the number of enzyme turnovers completed before inhibition, on the concentrations of 3-nitropropionate carbanion and succinate are those expected for an active site-directed and irreversible inhibitor. (ii) The inactivated enzyme is not resuscitated by centrifugation and washing of the mitochondria, in contrast to malonate-treated enzyme, and malonate protects against irreversible, inhibition. (iii) The inhibitor species is 3-nitropropionate carbanion and no external nucleophile is required for inhibition. (iv) The respiratory rates, respiratory control ratios, and ADP/O ratios obtained with NAD-linked substrates are unaffected by 3-nitropropionate carbanion. These results show that 3-nitropropionate carbanion is a highly specific, time-dependent, and irreversible inhibitor of succinate dehydrogenase. By analogy with the reaction of nitroethane with D-amino acid oxidase, the data are consistent with the hypothesis that the carbanionic inhibitor forms a covalent N-5 adduct with the active site flavin. However, the precise mechanism of inactivation, as well as mechanistic extrapolations to the oxidation of succinate, must await the elucidation of the structure of the modified enzyme. We can now explain the toxicity of plants such as Indigofera endecaphylla for mammals and fowl as being due to the irreversible blockage of the Krebs cycle by 3-nitropropionate carbanion.

Animals↗
PubMedDate not supplied

Potential toxicity from prolonged anesthesia: a case report of a thirty-hour anesthetic.

Selection of anesthetics for prolonged administration must include consideration of potential toxicity resulting from extended exposure. This report deals with a patient undergoing a 30-hour anesthetic that included nitrous oxide (N2O) and isoflurane (9.7 MAC-hours). Serial serum inorganic fluoride levels obtained in the perioperative period demonstrated a peak fluoride level of 12.6 mumols occurring 27 hours after isoflurane was discontinued. Although higher than previously reported fluoride levels following isoflurane anesthesia in healthy adults (4 mumols), the current results are below those levels associated with renal abnormalities after prolonged enflurane anesthesia (34 mumols). In addition to outlining basic care guidelines for patients undergoing a prolonged anesthetic, this report discusses potential toxicity from prolonged exposure to both N2O and isoflurane. It concludes that isoflurane can be tolerated in doses up to 10 MAC-hours without fluoride toxicity but cautions against the use of N2O for periods longer than 24 hours.

Adult↗