Academic journal article Alcohol Health & Research World

Alcohol Metabolism

Academic journal article Alcohol Health & Research World

Alcohol Metabolism

Article excerpt

Alcohol can be metabolized in various organs, including the stomach, small intestine, and brain. Quantitatively, however, most alcohol metabolism occurs in the liver, primarily through processes that involve oxidation (see figure) (Ashak et al. 1991; Lieber 1990). The discussion here focuses on two important pathways of oxidative alcohol metabolism: the alcohol dehydrogenase (ADH) pathway and the cytochrome P450 pathway.

Alcohol Dehydrogenase Pathway

Most ingested alcohol is initially oxidized in the liver by the enzyme ADH. This enzyme strips two hydrogen atoms from each alcohol molecule, thereby converting the alcohol to acetaldehyde. An enzyme called aldehyde dehydrogenase (ALDH) subsequently converts the acetaldehyde to acetate, also by removing hydrogen. To facilitate these reactions, the hydrogen removed during oxidation must be transferred to a substance that can serve as a hydrogen acceptor. In the case of ADH and ALDH, this hydrogen acceptor is an enzyme "helper" (i.e., coenzyme) called nicotinamide adenine dinucleotide (NAD). Upon accepting hydrogen, NAD is said to become chemically "reduced" and is referred to as reduced NAD (or NADH). NADH, in turn, can relinquish its newly acquired hydrogen to other metabolic reactions, thereby becoming available once again as a hydrogen acceptor.

The regeneration of NAD from NADH occurs within mitochondria, structures within cells where most of the cell's energy is generated through a process that promotes the formation of reactive oxygen species (ROS). The acetate formed by ALDH can serve as fuel for the cell. The ratio of oxidized to reduced coenzymes can significantly affect the cell's metabolic balance. …

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