Pyruvic acid

Pyruvic acid (CH₃COCOOH) is an organic acid, a ketone, as well as the simplest of the alpha-keto acids. The carboxylate (COO⁻) anion of pyruvic acid, its Brønsted–Lowry conjugate base, CH₃COCOO⁻, is known as pyruvate, and is a key intersection in several metabolic pathways.

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

Pyruvate supplies energy to living 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 (fermentation).

Chemistry

In 1834, Théophile-Jules Pelouze distilled both tartaric acid (L-tartaric acid) and racemic acid (a mix of D- and L-tartaric acid) and isolated pyrotartaric acid (methyl succinic acid^[2]) and another acid that Jöns Jacob Berzelius characterized the following year and named pyruvic acid.^[3] 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 anaerobic metabolism of glucose known as glycolysis.^[4] One molecule of glucose breaks down into two molecules of pyruvate^[4], 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. 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 called the citric 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. Pyruvate from glycolysis is converted by anaerobic respiration to lactate using the enzyme lactate dehydrogenase and the coenzyme NADH in lactate fermentation, or to acetaldehyde 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.

The pyruvic acid derivative bromopyruvic acid is being studied for potential cancer treatment applications by researchers at Johns Hopkins University in ways that would support the Warburg hypothesis on the cause(s) of cancer.

Pyruvate 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.

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

Pyruvate decarboxylation to acetyl CoA

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

Pyruvate carboxylation to oxaloacetate

Carboxylation by the pyruvate carboxylase produces oxaloacetate.

Transamination by the alanine aminotransferase

Reduction to lactic acid

Reduction by the lactate dehydrogenase produces lactic acid.

Interactive pathway map

Click on genes, proteins and metabolites below to link to respective articles.^[5]

See also

• Pyruvate scale

Notes

References

• Cody, G. D.; Boctor, N. Z.; Filley, T. R.; Hazen, R. M.; Scott, J. H.; Sharma, A.; Yoder, H. S.; Jr, (2000). "Primordial Carbonylated Iron-Sulfur Compounds and the Synthesis of Pyruvate". Science 289 (5483): 1337–1340. Bibcode 2000Sci...289.1337C. doi:10.1126/science.289.5483.1337. PMID 10958777.  edit