Alcohol dehydrogenase is our primary defense against alcohol, a toxic molecule that depresses the nervous system. High concentrations of alcohol dehydrogenase in the liver and stomach detoxify about approximately one ounce of liquor per hour. The alcohol is converted to acetaldehyde by the oxidation of NAD+ to NADH. Acetaldehyde is even more toxic to the body than ethanol. The body quickly convertes the acetaldehyde into acetate and other molecules that are easily utilized by the cell. Ethanol is not the only target of these enzymes, they also make important modifications to retinol, steroids, and fatty acids.
The NAD Cofactor
Molecular Model of Alcohol Dehydrogenase
Alcohol dehydrogenase is an 80kD protein that functions as a dimer in the cell. It is composed of identical alpha and beta chains.
Alpha and Beta chains
Each chain is composed of 374 residues, composing 12 alpha helices and 19 beta sheets.
NAD within the alcohol dehydrogenase subunit
The active site of alcohol dehydrogenase contains a zinc ion that is coordinated to the sulfur atoms of two cysteine residues and a histidine nitrogen atom. The Zn2+ polarizes the carbonyl group of the substrate to stabilize the transition state.
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