– Alcohol dehydrogenase class 4 mu/sigma chain (ADH7) is a cytoplasm enzyme which is a member of the alcohol dehydrogenase family. The expression of this gene makes it much more abundant in the stomach than the liver, thus it differs from the other known gene family members. ADH7 may participate in the synthesis of retinoic acid, a hormone important for cellular differentiation. Medium-chain (octanol) and aromatic (m-nitrobenzaldehyde) compounds are the best substrates. Ethanol is not a good substrate but at the high ethanol concentrations reached in the digestive tract, it plays a role in the ethanol oxidation and contributes to the first pass ethanol metabolism.