Acide malique

Résumé

L'acide malique est un acide dicarboxylique alpha-hydroxylé de formule . Il existe sous la forme de deux diastéréoisomères, les énantiomères L et D ; seul l'acide L-malique est présent dans le milieu naturel. La base conjuguée de l'acide malique et ses sels sont appelés malates. L'anion L-malate est un intermédiaire du cycle de Krebs, l'une des voies métaboliques majeures de respiration cellulaire chez presque tous les êtres vivants, et intervient dans le cycle de Calvin, qui entre dans le cadre de la photosynthèse. L'acide L-malique est très répandu dans le règne végétal et naturellement présent dans les pommes, les poires et le jus de raisin, dont il contribue à la saveur agréable. Il est de ce fait utilisé comme additif alimentaire, sous le numéro . Biochimie Le L-malate joue un rôle important en biochimie comme intermédiaire participant à plusieurs réactions structurantes du métabolisme cellulaire. Dans la fixation du carbone en , le L-malate est une source de dans le

Source officielle

https://fr.wikipedia.org/wiki/Acide_malique

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Yuzu is a citrus fruit cultivated mainly in northeast Asia. Due to the huge gastronomic interest emerging in recent years, some attempts to grow yuzu in Europe are being made. Juice and peel of yuzu cultivated in Switzerland have been characterised in this study. Peel constituted the major part of yuzu fruit followed by flesh, juice and seeds. The fruit degree of maturity was investigated by measuring pH, total titratable acidity and total soluble solids of the juice. The analyses were pursued by determining the content of vitamin C, malic and citric acids amounting to 0.560, 6.18 and 44.7 g/L, respectively. Four flavanones: naringin, hesperidin, naringenin, and hesperetin were identified and quantified in both juice and peel. The most abundant flavanone was hesperidin with 47 mu g/mL and 640 mu g/g dry matter (DM) in juice and peel, respectively. For the first time yuzu grown in Switzerland have been analysed and the obtained values have been compared with literature for other citrus fruits. Yuzu juice showed higher contents of citric and malic acid. Yuzu cultivated in Switzerland contained nearly twice as much vitamin C as yuzu juices from different regions of Japan. The content of vitamin C of yuzu was as high or higher than in most other citrus fruits. Large differences in the content of flavanones in yuzu juice from different regions of Japan were reported, in general the values noted were lower than those in the present study.

2018

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Production of a thermostable fumarase in Saccharomyces cerevisiae for the bioconversion of fumarate to L-malate

Coralie Signorell

The gene encoding fumarase (fum) from Thermus thermophilus was expressed in yeast Saccharomyces cerevisiae. The recombinant cells were heated at 70°C to inactivate indigenous enzymes and used for the bioconversion of fumaric acid to L-malic acid. By heating the host cells at 70°C, substrate is able to go across the heat-damaged membrane of the microorganism and a desired product can be formed. This new concept, called Synthetic Metabolic Engineering (SME), has already been applied successfully in Escherichia coli. Unfortunately, E. coli membrane is weakened too much during the heat treatment and enzyme leakage appears. The surface structure of yeast is more rigid than that of E. coli and this might be taken as an advantage for application of SME. When continuous or repeated-batch reaction is carried out, enzyme leakage becomes a major drawback. It is assumed that yeast cells could overcome this problem by retaining more enzymes in the cell during and after the heat treatment. In order to prove this hypothesis, a thermophilic fumarase (FUM) was over-expressed in two hosts, S. cerevisiae as well as E. coli. fum was first modified to be over-expressed in yeast cells and FUM was successfully produced in yeasts. Optimization of SME techniques was carried out for yeast cells. Then, enzyme activity and enzyme leakage was investigated for both strains. E. coli showed high level of FUM expression, though considerable amount of enzyme leaked to supernatant. On the other hand, even though the level of FUM expression in S. cerevisiae was low, yeast cells overcome leakage problem and are re-usable. This study showed the first trial of SME in yeast cells and possibility of utilization of yeast as a host strain for SME.

2011

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Aqueous organometallic catalysis. Isotope exchange reactions in H-2-D2O and D-2-H2O systems catalyzed by water-soluble Rh- and Ru-phosphine complexes

Gabor Laurenczy

The water-soluble complexes [{RuCl2(mTPPMS)(2)}(2)], [RuCl2(PTA)(4)], [RhCl(mTPPMS)(3)], [RhCl(mTPPTS)(3)], and [RhCl(PTA)(3)] (mTPPMS=sodium salt of meta-sulfonatophenyl-diphenylphosphine, mTPPTS=sodium salt oftris(meta-sulfonatophenyl) phosphine, and PTA=1,3,5-triaza-7-phosphaadamantane) showed high catalytic activity (up to 1252 h(-1)) in the H-D isotope exchange reactions between H-2 and D2O or D-2 and H2O. The reactions took place at 20-70degreesC, 0.1-2 MPa H-2, and were strongly influenced by the pH. In the hydrogenation (with H-2) of unsaturated acids in D2O, the relative rates of H-D exchange, hydrogenation and deuteration were determined by the individual substrates and catalysts: in the reaction of maleic acid catalyzed by [RhCl(mTPPMS)(3)] only hydrogenation took place with no deuteration and H-D exchange, whereas a similar reaction of itaconic acid was accompanied by a fast H-D exchange and the product methylsuccinic acid was highly deuterated.

2003

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