Citric acid

About: Citric acid is a research topic. Over the lifetime, 17745 publications have been published within this topic receiving 277125 citations. The topic is also known as: citrate & H3cit.

Biosynthesis of asymmetric citric acid; a substantiation of the Ogston concept.

Abstract: A. G. OGSTON1, in a recent note in Nature on the “Interpretation of Experiments on Metabolic Processes, using Isotopic Tracer Elements", introduced the important concept that an enzyme might be able to distinguish between the chemically ‘identical’ groups of a symmetrical compound. Ogston pointed to the dangers of the contrary assumption, and as one example he questioned the conclusion that citric acid was not an intermediate in the Krebs cycle of oxidations in so far as this conclusion was based upon the finding that the fixation of isotopically labelled carbon dioxide led to the formation of asymmetrically labelled α-keto-glutaric acid. It had been assumed2,3,4 that if citric acid were on the pathway leading to α-ketoglutaric acid, the latter would have had isotopic carbon equally distributed between the two carboxylic acid groups.

In vitro antilisterial effects of citrus oil fractions in combination with organic acids.

Abstract: The objectives of this study were to screen activity of citrus essential oil fractions (EOs) alone and in combination with organic acids against 2 species of Listeria. Five citrus EOs were initially screened by disc diffusion assay for antibacterial activity. Cold pressed terpeneless Valencia orange oil (CP terpeneless oil) had the strongest bacteriostatic (MIC) and bactericidal (MBC) properties at 0.55% and 1.67%, respectively. Four organic acids were tested for effectiveness against Listeria. Citric and malic acids proved to be the most effective with MBC of 1.1% alone. Assays were conducted to determine synergistic effects of EOs and citric or malic acids. There was a significant decrease in MIC and MBC to 0.04% EO plus 0.12% malic or citric acid. EOs from citrus paired with organic acids offer the potential as an all-natural antimicrobial for improving the safety of all-natural foods.

Overexpression of cytosolic malate dehydrogenase (MDH2) causes overproduction of specific organic acids in Saccharomyces cerevisiae.

Abstract: Saccharomyces cerevisiae accumulates l-malic acid through a cytosolic pathway starting from pyruvic acid and involving the enzymes pyruvate carboxylase and malate dehydrogenase. In the present study, the role of malate dehydrogenase in the cytosolic pathway was studied. Overexpression of cytosolic malate dehydrogenase (MDH2) under either the strong inducible GAL10 or the constitutive PGK promoter causes a 6- to 16-fold increase in cytosolic MDH activity in growth and production media and up to 3.7-fold increase in l-malic acid accumulation in the production medium. The high apparent Km of MDH2 for l-malic acid (11.8 mM) indicates a low affinity of the enzyme for this acid, which is consistent with the cytosolic function of the enzyme and differs from the previously published Km of the mitochondrial enzyme (MDH1, 0.28 mM). Under conditions of MDH2 overexpression, pyruvate carboxylase appears to be a limiting factor, thus providing a system for further metabolic engineering of l-malic acid production. The overexpression of MDH2 activity also causes an elevation in the accumulation of fumaric acid and citric acid. Accumulation of fumaric acid is presumably caused by high intracellular l-malic acid concentrations and the activity of the cytosolic fumarase. The accumulation of citric acid may suggest the intriguing possibility that cytosolic l-malic acid is a direct precursor of citric acid in yeast.