Citrate 158551 223192590 2008-07-02T23:57:23Z 72.178.241.230 [[Image:Citrate-2D-skeletal.png|thumb|The citrate anion]] [[Image:Citrate-3D-balls.png|thumb]] A '''citrate''' can refer either to the [[conjugate base]] of [[citric acid]], (C<sub>3</sub>H<sub>5</sub>O(COO)<sub>3</sub><sup>3&minus;</sup>), or to the [[ester]]s of citric acid. An example of the former, a [[salt (chemistry)|salt]] is [[trisodium citrate]]; an ester is [[trimethyl citrate]]. ==Other citric acid ions== Since citric acid is a multifunctional [[acid]], intermediate ions exist, '''hydrogen citrate''' ion, HC<sub>6</sub>H<sub>5</sub>O<sub>7</sub><sup>2&minus;</sup> and '''dihydrogen citrate''' ion, H<sub>2</sub>C<sub>6</sub>H<sub>5</sub>O<sub>7</sub><sup>&minus;</sup>. These may form salts as well, called [[acid salt]]s. ==pH== Salts of the hydrogen peroxide citrate ions are weakly acidic, while salts of the citrate ion itself (with an inert cation such as sodium ion) are weakly basic. ==Buffering== Citrate is a key component in the commonly used SSC 20X hybridization buffer. There exists authoritative literature (Maniatis) that incorrectly instructs the preparation of this buffer to include 3M NaCl and 0.3M Sodium Citrate, to be [[titration|titrated]] up with NaOH to a pH of 7. When the two components are actually mixed together, the pH is slightly basic. Therefore, the pH of the solution should instead be titrated down to 7 with HCl. Citric acid can act as a mild chelating agent. ==Metabolism== ===TCA cycle=== 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]]<sup>+</sup>, 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. ''See also [[TCA cycle]]'' ===Role in Glycolysis=== High concentration of citrate can inhibit [[phosphofructokinase]], the pace-maker of [[glycolysis]]. {{metabolism-stub}} {{citric acid cycle}} {{Antithrombotics}} [[Category:Carboxylate anions]] [[Category:Citrates]] [[es:Citrato]] [[pl:Cytryniany]] [[pt:Citrato]] [[ru:Цитрат]] [[su:Sitrat]]