Oxidized glutathione, also known as glutathione disulfide or GSSG, belongs to the class of organic compounds known as peptides. Peptides are compounds containing an amide derived from two or more amino carboxylic acid molecules (the same or different) by the formation of a covalent bond from the carbonyl carbon of one to the nitrogen atom of another. Oxidized glutathione is a very strong basic compound (based on its pKa). In humans, oxidized glutathione is involved in the metabolic disorder called leukotriene C4 synthesis deficiency pathway. Outside of the human body, oxidized glutathione has been detected, but not quantified in, several different foods, such as leeks, star anises, mamey sapotes, climbing beans, and common persimmons. This could make oxidized glutathione a potential biomarker for the consumption of these foods. Oxidized glutathione is a glutathione dimer formed by a disulfide bond between the cysteine sulfhydryl side chains during the course of being oxidized. Glutathione participates in leukotriene synthesis and is a cofactor for the enzyme glutathione peroxidase. It is also important as a hydrophilic molecule that is added to lipophilic toxins and waste in the liver during biotransformation before they can become part of the bile. Glutathione is also needed for the detoxification of methylglyoxal, a toxin produced as a by-product of metabolism. This detoxification reaction is carried out by the glyoxalase system. Glyoxalase I (EC 4.4.1.5) catalyzes the conversion of methylglyoxal and reduced glutathione into S-D-lactoyl-glutathione. Glyoxalase II (EC 3.1.2.6) catalyzes the hydrolysis of S-D-lactoyl-glutathione into glutathione and D-lactate.