Citrate

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Citrate

A citrate can refer either to the conjugate base of citric acid

Citric acid

Citric acid is a weak organic chemistry acid, and it is a natural preservative and is also used to add an acidic, or sour, taste to foods and soft drinks....
, (C₃H₅O(COO)₃³⁻), or to the ester

Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
s of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate

Triethyl citrate

Triethyl citrate is an ester of citric acid. It is a colorless, odorless liquid used as a food additive to stabilize foams, especially as whipping aid for egg white....
.

e citric acid is a multifunctional acid

Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
, intermediate ions exist, hydrogen citrate ion, HC₆H₅O₇²⁻ and dihydrogen citrate ion, H₂C₆H₅O₇⁻.

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Encyclopedia

A citrate can refer either to the conjugate base of citric acid

Citric acid

Ester

Triethyl citrate

Triethyl citrate is an ester of citric acid. It is a colorless, odorless liquid used as a food additive to stabilize foams, especially as whipping aid for egg white....
.

Other citric acid ions

Since citric acid is a multifunctional acid

Acid

Acid salt

Acid salts are a class of salt formed when a dibasic or tribasic acid has been neutralization to some degree. Because the acid is only partially neutralized, one or more replaceable protons remain....
s.

Acidity-Basicity

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

As a weak acid, citrate can be used as a component in buffer solution

Buffer solution

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of acid or base is added to it....
s, including the commonly used SSC 20X hybridization buffer. 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 describe solutions of citrate and acid for buffer pHs of between 3.0 and 6.2.

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

Thiamine pyrophosphate

Thiamine pyrophosphate , or thiamine diphosphate , is a thiamine Derivative which is produced by the enzyme thiamine pyrophosphatase. Thiamine pyrophosphate is a coenzyme that is present in all living systems, in which it catalyzes several Biochemistry reactions....
, lipoamide

Lipoamide

Lipoamide is a trivial name for 6,8-dithiooctanoic amide. It is lipoic acid's functional form where the carboxyl group is attached to protein by an amide linkage to an amino acid....
, FAD, NAD⁺, and CoA

COA

COA can refer to:*Cambridge Occupational Analysts*Cash on Arrival *Cause of action*CedarOpenAccounts COA *Center of Attention*Certificate of Approval for marriage or civil partnership in the United Kingdom...
), citrate synthase

Citrate synthase

The enzyme citrate synthase exists in nearly all living cells and stands as a pace-making enzyme in the first step of the Citric Acid Cycle . Citrate synthase is localized within eukaryotic cells in the mitochondrial matrix, but is encoded by nuclear DNA rather than mitochondrial....
catalyzes the condensation of oxaloacetate with Acetyl CoA to form citrate. Citrate continues in the TCA cycle via aconitase

Aconitase

Aconitase is an enzyme that catalyses the stereochemistry isomerization of citrate to isocitrate via cis-aconitate in the tricarboxylic acid cycle, a non-redox-active process....
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

Acetyl-CoA carboxylase

Acetyl-CoA carboxylase is a biotin-dependent enzyme that catalyzes the irreversible carboxylation of acetyl-CoA to produce malonyl-CoA through its two catalytic activities, biotin carboxylase and carboxyltransferase ....
, 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 enzyme which is allosterically modulated by citrate.

See also TCA cycle

Role in Glycolysis

High concentration of citrate can inhibit phosphofructokinase

Phosphofructokinase

Phosphofructokinase-1 is the most important regulatory enzyme of glycolysis. It is an allosteric enzyme made of 4 subunits and controlled by several activators and Enzyme inhibitors....
, the pace-maker of glycolysis

Glycolysis

Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, C3H5O3-....
.