Alcohol and Aldehyde Dehydrogenases in the Gastrointestinal Tract
The existence of ethanol metabolism in the gastrointestinal tract depends on the presence of suitable enzymatic systems to oxidize the alcohol to aldehyde. This chapter describes the functional and structural characteristics of the gastrointestinal forms of both dehydrogenases and their distribution in human gut. Data from the rat species are also included where the corresponding information from the human enzyme is not available. Alcohol dehydrogenase (ADH) of human stomach was investigated several years ago, and the presence of distinct isozymes was clearly recognized. The chapter also describes the properties of the enzyme forms that have been usually detected in human digestive tract. A functional new ADH gene, designated ADH6, has been characterized and the deduced amino acid sequence showed about 60% positional identity with known human ADHs. Activity analysis and immunohistochemical techniques show that the mucosa is the layer with higher ADH content throughout the gastrointestinal tract. Different parameters have been found to influence gastric ADH activity.