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The last steps of alcoholic fermentation in bacteria, plants, and yeast involve the conversion of pyruvate into acetaldehyde and carbon dioxide by the enzyme pyruvate decarboxylase, followed by the conversion of acetaldehyde into ethanol. The latter reaction is again catalyzed by an alcohol dehydrogenase, now operating in the opposite direction.
In addition to the toxicity of ethanol, the main psychoactive component of alcoholic beverages, other physiological symptoms may arise from the activity of acetaldehyde, a metabolite of alcohol. [11] These effects may not arise until hours after ingestion and may contribute to a condition colloquially known as a hangover.
The mechanism of ALD is not completely understood. 80% of alcohol passes through the liver to be detoxified. Chronic consumption of alcohol results in the secretion of pro-inflammatory cytokines (TNF-alpha, interleukin 6 and interleukin 8), oxidative stress, lipid peroxidation, and acetaldehyde toxicity.
IUPAC name IARC carcinogen group Toxic metabolite(s) Alcohol by volume (ABV) [1] LD50 in rat, oral [2]; Ethanol: Group 1: Acetaldehyde → acetic acid Up to 95.6% in rectified spirit
The alcohol tolerance is also connected with activity of alcohol dehydrogenases (a group of enzymes responsible for the breakdown of alcohol) in the liver, and in the bloodstream. High level of alcohol dehydrogenase activity results in fast transformation of ethanol to more toxic acetaldehyde.
The idea that acetaldehyde is the cause of the flush is also shown by the clinical use of disulfiram (Antabuse), which blocks the removal of acetaldehyde from the body via ALDH inhibition. The high acetaldehyde concentrations described share similarity to symptoms of the flush (flushing of the skin, accelerated heart rate, shortness of breath ...
Alcohol metabolism. ALDH1 is an isozyme of aldehyde dehydrogenase.A structural mutation in the gene of ALDH1, commonly found in East Asians, results in low levels of functional ALDH1 enzyme and thus, higher blood acetaldehyde levels.
The reaction uses NAD + to convert the ethanol into acetaldehyde (a toxic carcinogen). The enzyme acetaldehyde dehydrogenase (aldehyde dehydrogenase 2 family ALDH2, EC 1.2.1.3) then converts the acetaldehyde into the non-toxic acetate ion (commonly found in acetic acid or vinegar). [4] [6] This ion is in turn is broken down into carbon dioxide ...