Decarboxylation of Keto Acids

Enzyme-catalyzed decarboxylation of a keto acid is an important type of reaction in biochemistry. Organic chemists also use reactions involving decarboxylation of keto acids to make certain organic halides and other compounds.

Types

A keto acid is a type of organic compound that contains a ketone group and a carboxyl group. A carboxyl group consists of a carbon double-bonded to one oxygen and single-bonded to a hydroxyl group (OH). A ketone group consists of a carbonyl group (a carbon double-bonded to an oxygen) bonded to one carbon on either side. A ketone group is different from an aldehyde group, which is also a carbonyl group, but unlike a ketone group, occurs at the end of a carbon chain.

Function

In a decarboxylation reaction, the carboxyl group is removed from the keto acid, yielding carbon dioxide gas. The carboxyl group is then replaced with a hydrogen atom at the end of the carbon chain.

Significance

A number of reactions that occur in cells involve enzyme-catalyzed decarboxylation of a keto acid. Among the most important of these is the conversion of pyruvate (the anion of pyruvic acid) into acetyl-coenzyme A. Pyruvate is produced by the breakdown of sugar molecules, like glucose through glycolysis, then converted into acetyl coenzyme A by reactions catalyzed by three enzymes, one of which is pyruvate dehydrogenase. Acetyl coenzyme A in turn is fed into the citric acid cycle, an important pathway in cellular respiration.

References

• Michigan State University: Carboxylic acids
• ChemGuide UK: Decarboxylation of carboxylic acids and their salts
• "Marks' Basic Medical Biochemistry"; Michael A. Lieberman, Michael Lieberman, Allan D. Marks; 2008.