Pyruvic acid is a 3-carbon alpha-keto acid that is an intermediate in several important metabolic pathways. It is the simplest of all alpha-keto acids, containing a carbonyl group C{double bond}O on the middle carbon. Pyruvic acid (in its salt form pyruvate) is formed in the normal metabolism of glucose as a product of the glycolysis metabolic pathway. In a series of enzyme catalyzed reactions, the six carbon sugar is converted to two molecules of pyruvate that are further metabolized, with the loss of carbon dioxide, to two molecules of acetyl coenzyme A. Acetyl coenzyme A is fed into the aerobic Krebs cycle where it is further converted to carbon dioxide and water. In anaerobic conditions, pyruvate may accept hydrogen atoms that would otherwise be transferred to oxygen and thereby be converted to lactic acid. Lactic acid serves as an endpoint for glucose metabolism and may accumulate in tissues, sometimes to toxic levels. Pyruvate can be converted to the amino acid alanine by replacing the carbonyl group with an amino group (NH2). In the Hatch-Slack photosynthetic pathway, pyruvate plays an important role as a precursor to phosphoenolpyruvate, the molecule that serves as an acceptor of carbon dioxide.