Pyruvic acid
Simplest of the alpha-keto acids
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Through Carboxylic acid, Ketone and Glucose
Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates (such as glucose) via gluconeogenesis, or converted to fatty acids through a reaction via 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.
History
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. The correct molecular structure was deduced by the 1870s.
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Production
Pyruvic acid is prepared by treating tartaric acid with acid. It can also be produced by oxidation of propylene glycol by potassium permanganate or bleach. The hydrolysis of acetyl cyanide, formed by reaction of acetyl chloride with potassium cyanide, represents yet another route:
- CH3COCN + 2 H2O → CH3COCOOH + NH3
Structure
Pyruvic acid crystallizes as the keto acid, not the enol. The six non-hydrogen atoms are nearly coplanar. More relevant to biochemistry is the structure of the pyruvate anion. Several salts of pyruvate have been examined by X-ray crystallography. These tests confirm that pyruvate anion also exists in the keto form.
Reactivity
As a simple, abundant and bifunctional compound, pyruvic acid has been shown to participate in many reactions. Pyruvate reacts with amino acids to give alanine by the process called transamination:
- CH3C(O)CO−2 + RCH2NH2 → CH3CH(NH2)CO−2 + RCHO
Pyruvic acid self-condenses to give zymonic acid, a cyclic dehydrated dimer:
- 2 CH3C(O)CO2H → (O=C)(HOC)(HC)C(CH3)(CO2H) + H2O
The dehydration can be induced by distillation of pyruvic acid. Zymonic acid in turn forms a variety of derivatives in aqueous solution.
Pyruvic acid is a precursor to several types of heterocycles. When treated with phenethylamine, it gives tetrahydroisoquinoline by a sequential condensation/acylation process (Bischler–Napieralski reaction). With ortho-phenylenediamine it condenses to give quinoxalines. Condensation with 4,5-diaminopyrimidine give hydroxypteridines.
Biochemistry
Pyruvate is important 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 in 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.
Pyruvic acid production by glycolysis
In the last step of 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.
Click on genes, proteins and metabolites below to link to respective articles.
Decarboxylation to acetyl CoA
Pyruvate decarboxylation by the pyruvate dehydrogenase complex produces acetyl-CoA.
Carboxylation to oxaloacetate
Carboxylation by pyruvate carboxylase produces oxaloacetate.
Transamination to alanine
Transamination by alanine transaminase produces alanine.
Reduction to lactate
Reduction by lactate dehydrogenase produces lactate.
Environmental chemistry
Pyruvic acid is an abundant carboxylic acid in secondary organic aerosols.
Uses
Aside from its major role in the functioning of living organisms, pyruvic acid is of interest as a reagent in the synthesis of specialized organic compounds as discussed above in the reactivity section.