Enzymes of the aldehyde ferredoxin oxidoreductase (AOR) family contain a tungsten cofactor and an 4Fe4S cluster and catalyse the interconversion of aldehydes to carboxylates. This family includes AOR, formaldehyde ferredoxin oxidoreductase (FOR), glyceraldehyde-3-phosphate ferredoxin oxidoreductase (GAPOR), all isolated from hyperthermophilic archea. carboxylic acid reductase found in clostridia. and hydroxycarboxylate viologen oxidoreductase from Proteus vulgaris, the sole member of the AOR family containing molybdenum. GAPOR may be involved in glycolysis. but the functions of the other proteins are not yet clear. AOR has been proposed to be the primary enzyme responsible for oxidising the aldehydes that are produced by the 2-keto acid oxidoreductases.