Combined 1H and 31P NMR studies of the rat brain in vivo: effects of altered intracellular pH on metabolism.
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Animals↗
Biomedical subjects
S M Fitzpatrick
Publications and source records attributed to S M Fitzpatrick.
Inhibition of glutamate-aspartate transaminase by beta-methylene-DL-aspartate.
beta-Methylene-DL-aspartate, a new beta, gamma-unsaturated amino acid, is an irreversible inhibitor of soluble pig heart glutamate-aspartate transaminase (Ki approximately 3 mM with respect to the L-form; limiting rate constant for inactivation approximately 0.4 min-1). The new amino acid is the most specific inhibitor of glutamate-aspartate transaminase thus far studied. It does not inactivate pig heart glutamate-alanine transaminase, soluble rat kidney glutamine transaminase K, gamma-aminobutyrate transaminase (from Pseudomonas fluorescens), glutamate decarboxylase (Escherichia coli), snake venom L-amino acid oxidase, or hog kidney D-amino acid oxidase. In addition, the following enzymes were not inhibited by beta-methylene-DL-aspartate in rat tissue homogenates: gamma-aminobutyrate transaminase (brain), tyrosine transaminase (liver), glutamine transaminase L (liver), asparagine, transaminase (liver), ornithine transaminase (liver) or branch-chain transaminase(s) (kidney). Intraperitoneal injection of beta-methylene-DL-aspartate into mice decreased kidney and liver glutamate-aspartate transaminase activities but had no effect on liver glutamate-alanine transaminase activity.
Amino Acid Oxidoreductases↗
Use of beta-methylene-D,L-aspartate to assess the role of aspartate aminotransferase in cerebral oxidative metabolism.
Several inhibitors of aspartate aminotransferase, a key enzyme of the malate-aspartate shuttle, were investigated for their effects on cerebral oxidative metabolism in vitro. beta-Methylene-D,L-aspartate (2 mM), aminooxyacetate (0.1 mM), and D,L-vinylglycine (20 mM) all significantly reduced the activity of aspartate aminotransferase and the rate of oxygen consumption of rat cerebral cortex slices respiring on glucose. In the presence of beta-methyleneaspartate, a one-to-one correlation was found between the degree of inhibition of tissue respiration and the degree of inhibition of transaminase activity. Slices of rat liver incubated in the presence of glucose and beta-methyleneaspartate showed a similar one-to-one relationship between inhibition of oxygen comsumption and inhibition of aspartate aminotransferase activity, whereas with rat kidney cortex slices, the inhibition of aspartate aminotransferase activity was greater than the inhibition of oxygen consumption. Structural analogs of beta-methyleneaspartate (D,L-beta-methyl-D,L-aspartate, gamma-methyl-D,L-glutamate, and alpha-methyl-D,L-didehydroglutamate) that did not inhibit the activity of aspartate aminotransferase similarly did not inhibit the rate of oxygen consumption by cerebral cortex slices. In the presence of beta-methyleneaspartate, pyruvate oxidation by cerebral cortex slices was inhibited to almost the same extent as was glucose oxidation, and the oxidation of succinate was decreased by approximately 20%. The artificial electron acceptor phenazine methosulfate (0.1 mM) only partially overcame the beta-methyleneaspartate-mediated inhibition of respiration with glucose as substrate. The content of ATP and phosphocreatine declined steadily in slices incubated with glucose and beta-methyleneaspartate. At 1 h the concentration of lactate and the lactate/pyruvate ratio, an indicator of the cytoplasmic redox state, increased threefold, whereas the concentrations of malate, citrate, and aspartate decreased. The findings are interpreted in the context of the hypothesis that enzymes common to the malate-aspartate shuttle and the tricarboxylic acid cycle are physically complexed in brain, so that inhibition of aspartate aminotransferase, a component of the complex, impedes the flow of carbon through both metabolic pathways.(ABSTRACT TRUNCATED AT 400 WORDS)
Aminooxyacetic Acid↗
Acyl-CoA: sn-glycerol-3-phosphate O-acyltransferase in rat brain mitochondria and microsomes.
The subcellular distribution of acyl-CoA: sn-glycerol-3-phosphate O-acyltransferase between brain mitochondria and microsomes was investigated. The activities associated with purified rat brain mitochondrial and microsomal preparations could be distinguished by differences in their acyl-CoA specificity, products of acylation, and sensitivity to N-ethylmaleimide, trypsin, acetone, and polymyxin B. It was concluded that both brain mitochondria and microsomes possess the acyltransferase.
Acetone↗
Some metabolic effects of ammonia on astrocytes and neurons in primary cultures.
Some metabolic effects on primary cultures of neurons or astrocytes were studied following acute or chronic exposure to pathophysiological concentrations (usually 3 mM) of ammonia. Three parameters were investigated: (1) 14CO2 production from 14C-labeled substrates [glucose, pyruvate, branched-chain amino acids (leucine, valine, isoleucine), and glutamate]; (2) interconversion between glutamate and glutamine; and (3) incorporation of label from labeled branched-chain amino acids into proteins. Neither acute nor chronic exposure to ammonia had any effect on 14CO2 production from [U-14C]glucose in astrocytes and neurons, whereas under certain conditions 14CO2 production from [1-14C]pyruvate in astrocytes was inhibited by ammonia. Production of 14CO2 from [1-14C]branched-chain amino acids was inhibited by acute, but stimulated by chronic, exposure to ammonia (3 mM) in astrocytes, with less effect in neurons. Production of 14CO2 from [1-14C]glutamate in both astrocytes and neurons was inhibited by acute exposure to ammonia. In astrocytes, glutamate levels tended to decrease and glutamine levels tended to increase following acute exposure to ammonia; in neurons, both glutamine and glutamate levels decreased. Protein content (per culture dish) increased in astrocytes but not in neurons, after chronic exposure to ammonia, possibly as a result of enhanced protein synthesis and/or by inhibition of protein degradation.
Amino Acids↗