Citrate

Citrate
The citrate anion
Citrate-3D-balls.png

A citrate can refer either to the conjugate base of citric acid, (C3H5O(COO)33−), or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.

Contents

Other citric acid ions

Since citric acid is a multifunctional acid, intermediate ions exist, hydrogen citrate ion, HC6H5O72− and dihydrogen citrate ion, H2C6H5O7. These may form salts as well, called acid salts.

Acidity

Salts of the hydrogen citrate ions are weakly acidic, while salts of the citrate ion itself (with an inert cation such as sodium ion) are weakly basic.

Buffering

As a weak acid, citrate can be used as a component in buffer solutions, including the commonly used SSC 20X hybridization buffer.[1] This buffer uses sodium citrate and sodium chloride to maintain a neutral 7.0 pH. Other buffers may use a mixture of sodium citrate and citric acid – canonical buffer tables compiled for biochemical studies[2] describe solutions of citrate and acid for buffer pHs of between 3.0 and 6.2.

Chelating

Citric acid can act as a mild chelating agent; citrate, usually in the form of trisodium citrate, may be given as an anticoagulant, because it chelates calcium ions, and therefore inhibits coagulation. Another application is in the form of iron(II) citrate as a nutritional supplement. Here, the benefit is the solubility as a chelate of the otherwise mostly insoluble iron.

Metabolism

Citrate is an intermediate in the TCA (Krebs) cycle. After the pyruvate dehydrogenase complex forms acetyl-CoA, from pyruvate and five cofactors (thiamine pyrophosphate, lipoamide, FAD, NAD+, and CoA), citrate synthase catalyzes the condensation of oxaloacetate with acetyl CoA to form citrate. Citrate continues in the TCA cycle via aconitase with the eventual regeneration of oxaloacetate, which can combine with another molecule of acetyl CoA and continue cycling.

Fatty acid synthesis

Citrate can also be transported out of the mitochondria and into the cytoplasm, then broken down into acetyl-CoA for fatty acid synthesis. Citrate is a positive modulator of this conversion, and allosterically regulates the enzyme acetyl-CoA carboxylase, which is the regulating enzyme in the conversion of acetyl-CoA into malonyl-CoA (the commitment step in fatty acid synthesis). In short, citrate is transported to the cytoplasm, converted to acetyl CoA, which is converted into malonyl CoA by the acetyl CoA carboxylase, which is allosterically modulated by citrate.

See also TCA cycle

Role in glycolysis

High concentrations of cytosolic citrate can inhibit phosphofructokinase, catalyst of one of the rate-limiting steps of glycolysis.

References

  1. ^ Maniatis et al., 1982.[clarification needed]
  2. ^ G. Gomori, Preparation of buffers for use in enzyme studies, 1955.



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  • citrate — [ sitrat ] n. m. • 1782; du lat. citrus ♦ Chim. Sel de l acide citrique. Citrate de sodium. ● citrate nom masculin Sel ou ester de l acide citrique. citrate n. m. CHIM Nom des sels et esters de l acide citrique. ⇒CITRATE, subst. masc. CHIM. Sel… …   Encyclopédie Universelle

  • Citrate — Cit rate, n. [From {Citric}.] (Chem.) A salt of citric acid. [1913 Webster] …   The Collaborative International Dictionary of English

  • Citrāte — Citrāte, Zitronensäuresalze, z. B. Natriumcitrat, zitronensaures Natron …   Meyers Großes Konversations-Lexikon

  • Citrate —   [lateinisch], Singular Citrat das, s, Zitrate, die Salze und Ester der Zitronensäure …   Universal-Lexikon

  • citrate — [si′trāt΄, sī′trāt΄] n. [ CITR(I) + ATE2] a salt or ester of citric acid …   English World dictionary

  • Citrate — Acide citrique Acide citrique …   Wikipédia en Français

  • citrate — 1. noun Any salt or ester of citric acid. See Also: ferric ammonium citrate, Benedicts solution, sildenafil citrate, Viagra 2. verb To cause to form citrate …   Wiktionary

  • CITRATE — n. m. T. de Chimie Nom générique des sels formés par la combinaison de l’acide citrique avec différentes bases. Les citrates, autres que le citrate de chaux et le citrate de magnésie, ne sont d’aucun usage …   Dictionnaire de l'Academie Francaise, 8eme edition (1935)

  • Citrate — Strukturformel Allgemeines Name Citronensäure Andere Namen Zitronens …   Deutsch Wikipedia

  • citrate — noun /ˈsɪtreɪt/ (say sitrayt), /ˈsaɪ / (say suy ) 1. a salt or ester of citric acid. –verb (t) /sɪˈtreɪt/ (say si trayt), /saɪˈtreɪt/ (say suy trayt) (citrated, citrating) 2. to treat with a citrate, especially with sodium citrate …   Australian-English dictionary

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