Alphaketobutyrate

Alphaketobutyrate, also known as alpha-ketobutanoic acid or 2-oxobutanoic acid, is a four-carbon alpha-keto acid. It is the alpha-keto analogue of butyric acid, having a carboxyl group at one end and a ketone on the adjacent (alpha) carbon, with the chemical formula C4H6O3.

Biological occurrence and synthesis: Alphaketobutyrate is an intermediate in amino acid catabolism, most notably formed in the degradation of threonine by threonine dehydratase, producing 2-oxobutyrate. It can also arise in related propionate pathways from methionine or valine metabolism. In many organisms, it is further metabolized to propionyl-CoA, which can enter the methylmalonyl-CoA pathway and ultimately feed into the tricarboxylic acid cycle as succinyl-CoA.

Metabolic roles: Alphaketobutyrate can participate in transamination reactions, serving as a keto partner to yield threonine or other amino acids. In some bacteria, it also participates in isoleucine biosynthesis as a carbon skeleton that combines with acetyl-CoA-derived units to form longer-chain amino acid precursors. Thus, alphaketobutyrate functions as an intermediate link between threonine catabolism, propionate metabolism, and broader amino acid biosynthesis pathways.

Chemical properties and applications: The compound is typically studied and used in laboratory settings as the free acid or as salts (for example, sodium alphaketobutyrate). It is a small, water-soluble molecule that participates in enzyme assays and metabolic studies involving alpha-keto acids and aminotransferases. Handling follows standard laboratory safety practices for irritant organic acids.

See also: 2-oxobutanoic acid; alpha-keto acids; threonine metabolism.