Methylglyoxal, also called pyruvaldehyde or 2-oxo-propanal (CH3-CO-CH=O or C3H4O2) is the aldehyde form of pyruvic acid. Methylglyoxal is both an aldehyde and a ketone. In the body, methylglyoxal may form from 3-amino acetone, which is an intermediate of threonine catabolism. This compound, as well as glyoxal, is a byproduct of metabolism, but cannot be used. The aldehyde reacts with glutathione, a tripeptide consisting of glutamic acid, cysteine, and glycine. Glutathione reduces methylglyoxal to 1-hydroxy acetone, a ketol. 1-Hydroxy acetone goes through enediol tautomerism to lactaldehyde. Then the lactaldehyde is oxidised by glutathione to D-lactic acid. Methylglyoxal is also called a ketal, because it has an aldehydic and ketonic carbonyl group. It is a type of the advanced glycation endproducts (AGEs) resulting from sugar modifications, such as the Maillard reaction. When the reductone is cleaved, pyruvaldehyde forms.