Any carboxylic acid that also contains a ketone (carbonyl) group
Definition #2 for "keto acid"
Keto acids are organic compounds that contain a carboxylic acid group and a ketone group. 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 and in glycolysis. Common types of keto acids include: ⁕Alpha-keto acids, or 2-oxoacids, such as pyruvic acid, have the keto group adjacent to the carboxylic acid. Another important member is oxaloacetic acid, a component of the Krebs cycle. Alpha-ketoglutarate, is a 5-carbon keto acid derived from glutamic acid. Alpha-ketoglutarate participates in cell signaling by functioning as a cofactor for a variety of iron-containing redox enzymes, for example the proline hydroxylases that modify the hypoxia inducible factor leading to the destruction of HIF except in hypoxia when this pathway is blocked. ⁕Beta-keto acids, or 3-oxoacids, such as acetoacetic acid, have the ketone group at the second carbon from the carboxylic acid ⁕Gamma-keto acids, or 4-oxoacids, such as levulinic acid, have the ketone group at the third carbon from the carboxylic acid. When ingested sugars and carbohydrate levels are low, stored fats and proteins are the primary source of energy production. Glucogenic amino acids from proteins are converted to glucose and fats can be used to form ketone bodies. Ketogenic amino acids can be deaminated to produce alpha keto acids and ketone bodies.