Pyruvic acid

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Pyruvic acid

Names
Preferred IUPAC name 2-Oxopropanoic acid
Other names Pyruvic acid α-Ketopropionic acid Acetylformic acid Pyroracemic acid
Identifiers
CAS Number	127-17-3
3D model (JSmol)	Interactive image
Abbreviations	Pyr
ChEBI	CHEBI:32816
ChEMBL	ChEMBL1162144
ChemSpider	1031
DrugBank	DB00119
ECHA InfoCard	100.004.387
IUPHAR/BPS	4809
KEGG	C00022
PubChem CID	1060
UNII	8558G7RUTR
CompTox Dashboard (EPA)	DTXSID2021650
Properties
Chemical formula	C3H4O3
Molar mass	88.06 g/mol
Density	1.250 g/cm3
Melting point	11.8 °C (53.2 °F; 284.9 K)
Boiling point	165 °C (329 °F; 438 K)
Acidity (pKa)	2.50
Related compounds
Other anions	pyruvate ion
Related keto-acids, carboxylic acids	acetic acid glyoxylic acid oxalic acid propionic acid acetoacetic acid
Related compounds	propionaldehyde glyceraldehyde methylglyoxal sodium pyruvate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Pyruvic acid (CH₃COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate (/paɪˈruːveɪt/), the conjugate base, CH₃COCOO⁻, is a key intermediate in several metabolic pathways throughout the cell.

Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates (such as glucose) via gluconeogenesis, or to fatty acids through a reaction with acetyl-CoA. It can also be used to construct the amino acid alanine and can be converted into ethanol or lactic acid via fermentation.

Pyruvic acid supplies energy to cells through the citric acid cycle (also known as the Krebs cycle) when oxygen is present (aerobic respiration), and alternatively ferments to produce lactate when oxygen is lacking (lactic acid fermentation).

Chemistry

In 1834, Théophile-Jules Pelouze distilled tartaric acid and isolated glutaric acid and another unknown organic acid. Jöns Jacob Berzelius characterized this other acid the following year and named pyruvic acid because it was distilled using heat. Pyruvic acid is a colorless liquid with a smell similar to that of acetic acid and is miscible with water. In the laboratory, pyruvic acid may be prepared by heating a mixture of tartaric acid and potassium hydrogen sulfate, by the oxidation of propylene glycol by a strong oxidizer (e.g., potassium permanganate or bleach), or by the hydrolysis of acetyl cyanide, formed by reaction of acetyl chloride with potassium cyanide: 

CH₃COCl + KCN → CH₃COCN + KCl

CH₃COCN → CH₃COCOOH

Biochemistry

Pyruvate is an important chemical compound in biochemistry. It is the output of the metabolism of glucose known as glycolysis. One molecule of glucose breaks down into two molecules of pyruvate, which are then used to provide further energy, in one of two ways. Pyruvate is converted into acetyl-coenzyme A, which is the main input for a series of reactions known as the Krebs cycle (also known as the citric acid cycle or tricarboxylic acid cycle). Pyruvate is also converted to oxaloacetate by an anaplerotic reaction, which replenishes Krebs cycle intermediates; also, the oxaloacetate is used for gluconeogenesis. These reactions are named after Hans Adolf Krebs, the biochemist awarded the 1953 Nobel Prize for physiology, jointly with Fritz Lipmann, for research into metabolic processes. The cycle is also known as the citric acid cycle or tricarboxylic acid cycle, because citric acid is one of the intermediate compounds formed during the reactions. 

If insufficient oxygen is available, the acid is broken down anaerobically, creating lactate in animals and ethanol in plants and microorganisms (and carp). Pyruvate from glycolysis is converted by fermentation to lactate using the enzyme lactate dehydrogenase and the coenzyme NADH in lactate fermentation, or to acetaldehyde (with the enzyme pyruvate decarboxylase) and then to ethanol in alcoholic fermentation.

Pyruvate is a key intersection in the network of metabolic pathways. Pyruvate can be converted into carbohydrates via gluconeogenesis, to fatty acids or energy through acetyl-CoA, to the amino acid alanine, and to ethanol. Therefore, it unites several key metabolic processes.

Reference ranges for blood tests, comparing blood content of pyruvate (shown in violet near middle) with other constituents.

Pyruvic acid production by glycolysis

In glycolysis, phosphoenolpyruvate (PEP) is converted to pyruvate by pyruvate kinase. This reaction is strongly exergonic and irreversible; in gluconeogenesis, it takes two enzymes, pyruvate carboxylase and PEP carboxykinase, to catalyze the reverse transformation of pyruvate to PEP. 

phosphoenolpyruvate	pyruvate kinase		pyruvate
	ADP	ATP
	ADP	ATP
	pyruvate carboxylase and PEP carboxykinase

Compound C00074 at KEGG Pathway Database. Enzyme 2.7.1.40 at KEGG Pathway Database. Compound C00022 at KEGG Pathway Database.

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Glycolysis and Gluconeogenesis

Decarboxylation to acetyl CoA

Pyruvate decarboxylation by the pyruvate dehydrogenase complex produces acetyl-CoA.

pyruvate	pyruvate dehydrogenase complex		acetyl-CoA
	CoA + NAD+	CO2 + NADH + H+

Carboxylation to oxaloacetate

Carboxylation by pyruvate carboxylase produces oxaloacetate. 

pyruvate	pyruvate carboxylase		oxaloacetate
	ATP + CO2	ADP + Pi

Transamination to alanine

Transamination by alanine transaminase produces alanine. 

pyruvate	alanine transaminase		alanine
	glutamate	α-ketoglutarate
	glutamate	α-ketoglutarate

Reduction to lactate

Reduction by lactate dehydrogenase produces lactate. 

pyruvate	lactate dehydrogenase		lactate
	NADH	NAD+
	NADH	NAD+

Uses

Pyruvate is sold as a weight-loss supplement, though credible science has yet to back this claim. A systematic review of six trials found a statistically significant difference in body weight with pyruvate compared to placebo. However, all of the trials had methodological weaknesses and the magnitude of the effect was small. The review also identified adverse events associated with pyruvate such as diarrhea, bloating, gas, and increase in low-density lipoprotein (LDL) cholesterol. The authors concluded that there was insufficient evidence to support the use of pyruvate for weight loss.

There is also in vitro as well as in vivo evidence in hearts that pyruvate improves metabolism by NADH production stimulation and increases cardiac function.