Acetaldehyde metabolic processes

Many biological processes involve oxidation of alcohols to carbonyl compounds or the reverse process reduction of carbonyl compounds to alcohols Ethanol for example is metabolized m the liver to acetaldehyde Such processes are catalyzed by enzymes the enzyme that catalyzes the oxidation of ethanol is called alcohol dehydrogenase... 

Two major pathways of alcohol metabolism to acetaldehyde have been identified (Figure 23-1). Acetaldehyde is then oxidized to acetate by a third metabolic process. 

After we have had a drink, the alcohol it contains is absorbed into the blood and enters the liver, where it is broken down by an enzyme (alcohol dehydrogenase) into a chemical called acetaldehyde. This is formed slowly, fortunately (as it is responsible for some of the unpleasant effects of alcoholic drinks, flushes, headache, nausea). Thankfully, it is also removed more rapidly by another enzyme (aldehyde dehydrogenase), to form acetic acid, which is then incorporated into normal metabolic processes, to produce energy for the body for example. 

Many redox enzymes used in BFCs require cofactors for catalysis. For example, yeast alcohol dehydrogenase catalyzes the oxidation of ethanol to acetaldehyde, with the concomitant reduction of NAD" to NADH. Most commonly, cofactor specificity has been engineered to increase the activity of NADP(H)-dependent enzymes with NAD(H) or to correct a cofactor imbalance in a metabolic process. As the NAD(H) cofactor is more stable and less expensive than NADP(H), this generally improves the economics of a process [42—44]. 

Alcohol is metabolized by alcohol dehydrogenase (a zero-order process except at very high and very low concentrations) to acetaldehyde, which is metabolize to carbon dioxide and water by aldehyde dehydrogenase. Catalase and the microsomal alcohol oxidase system are also involved. 

In most organisms undergoing aerobic metabolism, pyruvate is oxidized to acetyl-CoA in a complex process involving its decarboxylation (Eq. 10-6). This oxidative decarboxylation, like the decarboxylation of pyruvate to acetaldehyde, requires thiamin diphosphate. In addition, an array of other catalysts participate in the process (see Fig. 15-15). Among these are the electron carrier flavin adenine diphosphate (FAD), which is derived from the vitamin riboflavin. Like NAD+, this... 

Alcoholic fermentation occurs when the end product is ethanol, as shown in Figure 4.11. In this process the pyruvate is first converted enzymatically to acetaldehyde. The conversion of acetaldehyde to ethanol produces NAD+ from NADH + H+, and the NAD+ is cycled through the glycolysis process. As with lactic acid fermentation, the glycolysis process produces usable energy contained in two molecules of ATP produced for each molecule of glucose metabolized. 

H) lndole-3-acetaldehyde pathway The natural occurrence of indole-3-acetaldehyde (IAAld) in plants was first described in the extracts of cucumber seedlings98 where the concentration of IAAld was --(I. ngg-1 fresh weight. Possibly arising via IAOx or indole-3-pyruvate (IPyA), IAAld may act as a convergence point for tryptophan-dependent pathways.78 In an early study, the capacity to metabolize [14Ci]tryptophan via IPyA and IAAld was determined.99 Two primarily cytoplasmic enzymes were involved and the process was NAD-dependent. 

A rise in the NADH/NAD ratio and the associated increase in the redox potential as well as the formation of acetaldehyde result in a variety of metabolic disturbances in the hepatocellular oxidation processes, so that pathophysiological consequences can be observed. This large variety of alcohol-induced metabolic disturbances is responsible for many situations of clinical importance, and thus acute and chronic alcohol abuse will eventually result in additional metabolic complications, (s. tab. 28.2)... 

Ethanol is metabolized in a two step process (see figure below), according to zero order kinetics. As the drug passes through the liver, it is first dehydrated by alcohol dehydrogenase, forming acetaldehyde (which dissociates into methanol and formaldehyde, should the next metabolic step be inhibited). Acetaldehyde is then metabolized by aldehyde dehydrogenase into acetate, which may then enter the citric acid cycle. 

The interaction between alcohol and vitamin A is complex. They have overlapping metabolic pathways a similar 2-step process is involved in the metabolism of both alcohol and vitamin A, with alcohol dehydrogenases and acetaldehyde dehydrogenases being implicated in the conversion of vitamin A to retinoic acid. Alcohol appears to act as a competitive inhibitor of vitamin A oxidation. In addition, chronic alcohol intake can induce cytochrome P450 isoenzymes that appear to increase the breakdown of vitamin A (retinol and retinoic acid) into more polar metabolites in the liver, which can cause hepatocyte death. So chronic alcohol consumption may enhance the intrinsic hepatotoxicity of high-dose vitamin A. Alcohol has also been shown to alter retinoid homoeostasis by increasing vitamin A mobilisation from the liver to extrahepatic tissues, which could result in depletion of hepatic stores of vitamin A. ... 

In our body, toxic chemicals are metabolized in the liver. One such process involves the production of acetaldehyde from ethanol. This conversion is best described as ... 

The liver contains an enzyme called alcohol dehydrogenase, which is responsible for metabolizing ethemol. Alcohol dehydrogenase converts the ethanol to einother molecule called acetaldehyde, which is then excreted from the body. A heedthy liver can process about half an ounce of pure ethanol each hour, which equates to roughly one beer, one glass of wine, or an ounce of liquor each hour. 

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