HOOC(CH₂)₂C(O)COOH, a dicarboxylic α-keto acid. Readily soluble in water, it has a melting point of 115°-116°C. α-ketoglutaric acid is the intermediate product of carbohydrate, fat, and protein metabolism in animals, plants, and microorganisms. The important role of α-ketoglutaric acid in metabolism is determined by its participation in the Krebs cycle (tricarboxylic acid cycle). α-ketoglutaric acid is formed during the oxidation of isocitric acid as well as during the transamination (amino group transfer) and deamination (amino group loss) of glutamic acid. Simultaneously participating in protein and carbohydrate metabolism, α-ketoglutaric acid connects nitrogen exchange with the transformations of fats and carbohydrates.