In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, keto acids or ketoacids (also called oxo acids or oxoacids) are
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
s that contain a
carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...
group () and a
ketone
In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
group ().
[Franz Dietrich Klingler, Wolfgang Ebertz "Oxocarboxylic Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. ] In several cases, the keto group is hydrated. The alpha-keto acids are especially important in biology as they are involved in the
Krebs citric acid cycle
The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of chemical reaction, biochemical reactions that release the energy stored in nutrients through acetyl-Co ...
and in
glycolysis
Glycolysis is the metabolic pathway that converts glucose () into pyruvic acid, pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The Thermodynamic free energy, free energy released in this process is used to form ...
.
Common types of keto acids include:
*Alpha-keto acids, alpha-ketoacids, or 2-oxoacids have the keto group adjacent to the carboxylic acid. They often arise by
oxidative deamination
Oxidative deamination is a form of deamination that generates α-keto acids and other oxidized products from amine-containing compounds, and occurs primarily in the liver. Oxidative deamination is stereospecific, meaning it contains different ster ...
of
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
s, and reciprocally, they are
precursor
Precursor or Precursors may refer to:
*Precursor (religion), a forerunner, predecessor
** The Precursor, John the Baptist
Science and technology
* Precursor (bird), hypothesized genus of fossil birds that was composed of fossilized parts of unre ...
s to the same. Alpha-keto acids possesses extensive chemistry as
acylation
In chemistry, acylation is a broad class of chemical reactions in which an acyl group () is added to a substrate. The compound providing the acyl group is called the acylating agent. The substrate to be acylated and the product include the foll ...
agents. Furthermore, alpha-keto acids such as
phenylpyruvic acid
Phenylpyruvic acid is the organic compound with the formula C6H5CH2C(O)CO2H. It is a keto acid.
Occurrence and properties
The compound exists in equilibrium with its (''E'')- and (''Z'')-enol tautomers. It is a product from the oxidative deamin ...
are endogenous sources for
carbon monoxide
Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
(as a
gasotransmitter
Gasotransmitters is a class of neurotransmitters. The molecules are distinguished from other bioactive endogenous gaseous signaling molecules based on a need to meet distinct characterization criteria. Currently, only nitric oxide, carbon monoxid ...
) and pharmaceutical
prodrug
A prodrug is a pharmacologically inactive medication or compound that, after intake, is metabolized (i.e., converted within the body) into a pharmacologically active drug. Instead of administering a drug directly, a corresponding prodrug can be ...
scaffold. Important representatives:
**
pyruvic acid
Pyruvic acid (CH3COCOOH) is the simplest of the keto acids, alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is an metabolic intermediate, intermediate in several m ...
, pervasive intermediate in metabolism.
**
oxaloacetic acid
Oxaloacetic acid (also known as oxalacetic acid or OAA) is a crystalline organic compound with the chemical formula HO2CC(O)CH2CO2H. Oxaloacetic acid, in the form of its conjugate base oxaloacetate, is a metabolic intermediate in many processes ...
, a component of the
Krebs cycle
The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of biochemical reactions that release the energy stored in nutrients through acetyl-CoA oxidation. The e ...
.
**
alpha-ketoglutaric acid, a 5-carbon ketoacid derived from
glutamic acid
Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α- amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can ...
. Alpha-ketoglutarate participates in
cell signaling
In biology, cell signaling (cell signalling in British English) is the Biological process, process by which a Cell (biology), cell interacts with itself, other cells, and the environment. Cell signaling is a fundamental property of all Cell (biol ...
by functioning as a coenzyme. It is commonly used in transamination reactions.
*Beta-keto acids, beta-ketoacids, or 3-oxoacids, such as acetoacetic acid, have the ketone group at the second carbon from the carboxylic acid. They generally form by the Claisen condensation. The presence of the keto group at the beta position allows them to easily undergo thermal decarboxylation.
*Gamma-keto acids, Gamma-ketoacids, or 4-oxoacids have the ketone group at the third carbon from the carboxylic acid. Levulinic acid is an example.
Keto acids appear in a wide variety of anabolic pathways in metabolism. For instance, in plants (specifically, in Conium maculatum, hemlock, pitcher plants, and fool's parsley), 5-oxo-octanoic acid is converted in enzymatic and non-enzymatic steps into the cyclic compound, cyclic class of coniine alkaloids.
When ingested sugars and carbohydrate levels are low, stored fats and proteins are the primary source of energy production. Glucogenic amino acids from proteins and/or Glycerol from Triglycerides are converted to glucose. Ketogenic amino acids can be deaminated to produce alpha keto acids and ketone bodies.
Alpha keto acids are used primarily as energy for liver cells and in fatty acid synthesis, also in the liver.
See also
*Ulosonic acids
*Pseudoacid
References
External links
*
{{Authority control
Keto acids,