The oxidation of alcohol

Biochemistry oxidation of alcohol is as follows: alcohol→acetaldehyde→acetate→water + carbon dioxide. (acetyl-COA)
The first stage of this process of oxidation of ethanol to acetaldehyde. This process in the body can be done in three ways. It catalyze soluble enzymes alcohol dehydrogenase, microsomal atalakitasa system, catalase-peroxidase system (Fig. 2).


Fig. 2. The usual relationship ways oxidation of alcohol in the body

Alcoholdehydrogenase (ADH) human liver has been studied relatively well. This enzyme with a molecular mass of about 85 000-87 000 consists of two subunits and at low concentrations of ethanol in the body oxidation carries out only one of them. At high concentrations of ethanol are already both subunit of ADH. It has been suggested that ethanol is not the best substrate for ADH. In the body substrates ADH serve as primary and secondary aliphatic alcohols and aldehydes, ketones, aromatic alcohols and aldehydes, retinol and other unsaturated alcohols, diols, pantotenova wet alcohol, steroids and other (Ostrovsky and others, 1986).
Almost all of ADH is contained in the human liver, only a small quantity found in the intestinal tract, lungs, heart, kidneys. Found ADH and in the brain, but its activity is small and is only 0.025% of activity in the liver. In studies I. E. Lomako with co-authors (1985) shows that the properties of ADH brain is such that in physiological conditions enzyme practically can not participate in the oxidation of ethanol. In this regard, the functional value of ADH in nerve tissue can be attributed mainly to the fact that the enzyme does not function as dehydrogenase, and as reductase (in the system of ethanol acetaldehyde), protecting the brain from toxic acetaldehyde.
Fundamentally, the ADH activity is determined by the availability of a sufficient number of coenzyme - dinucleotide (NAD+). About this will be discussed below, when considering cases of chronic alcohol intake. Overall, about 80% of incoming ethyl alcohol is metabolized in the following way (Fig. 3).

diagram of the processes of oxidation of alcohol in the liver cell
Fig. 3. The General scheme of the processes of oxidation of alcohol in the liver cell (hepatocytes) (:Musil, 1984)
Of the traction system of transport of electrons (respiratory chain);
The Central laboratory is the citric acid cycle;
MAAS - microsomal atalakitasa system;
ADH - alcoholdehydrogenase;
OVER - adenine dinucleotide

Dissimilation occurs in the cytoplasm of the cell, and formed restored OVER (OVER-N) can be used for synthesis of adenosine triphosphate (ATP)and protonation (H+) other stages of oxidation-reduction processes in cells. The role of ATP in the body is unique. This connection belongs to the class of so-called makroergov - universal source of energy for the majority occur in the body processes related to energy consumption.
At high concentrations of alcohol on their oxidation connects microsomal atalakitasa system (MEOS)localized in the smooth endoplasmic reticulum of the liver cells (hepatocytes). In norm the role MEAS small, with a maximum of 20% of ethanol oxidation. Activity oxidase system microsomes revealed only in the presence of recovered nicotinoyldihydrocodeine (NADP·H) or NADP·H-generating systems. The reaction scheme is as follows:

Finally, the third way oxidation of alcohol is catalyzed by the enzyme catalase, with the participation of hydrogen peroxide (H2O2) and localized in peroksisomakh. The value of this reaction in the norm quite small (a few percent). The reaction scheme is as follows:

However, the role of this way of oxidation increases with higher concentrations of ethanol in the body.
The second important stage of oxidation - oxidation formed at the previous stage of acetaldehyde. We note a considerable detail: acetaldehyde much more active in biochemical ratio and more toxic than ethanol. It can cause psychotropic and toxic effects in doses of 100 - 200 times smaller than alcohol (Azrieli, 1968), and, having high neurotropic activity, may intervene in the synthesis of protein. Thus it is clear that the oxidation of ethanol, the body is looking forward to metabolize acetaldehyde.


As it happens?
The main link of this reaction is aldehyddehydrogenase (Aldh). Dependent ON+ Aldg widespread, and there is in the human body in the form of several isoenzymes. The most active isoenzyme Aldh-1.
Know an interesting fact. Noted that often the representatives of the Mongoloid race quickly and easily blushes after alcohol skin, and the intoxication sometimes introduces an element of discomfort. It turned out that Asia is often missing just isoenzyme Aldh-1 hinders speedy metabolism of alcohol. Naturally, this is an accumulation of intermediate product of oxidation of acetaldehyde, which stimulates the skin redness. And, considering the relatively low prevalence of alcoholism in Asia, it is quite possible that unpleasant flowing intoxication (in the absence Aldh-1) in some way and prevent the abuse of alcohol. But, according to other researchers, high sensitivity to the action of alcohol is associated with high activity of "atypical" ADH.
In aqueous solution acetaldehyde is equivalent mixture of free aldehyde and hydrate. In the process of dehydrogenation hydrate goes into acetate. The reaction scheme is as follows:

It is especially important to note the inclusion in the future acetate in two-carbon Fund (as acetilcoenzyme A) with subsequent metabolism to the final product is carbon dioxide and water.
And one more important circumstance. The oxidation of alcohol frees large amounts of energy -7,1 qual/year In respect of calorie alcohol is second only to the fats and able to meet part of the energy reserves of the body.
A certain role in the transformations of acetaldehyde in the body play a fusion reaction, what is happening in terms of increasing content of acetaldehyde. Probably, the part of acetaldehyde, which were not subjected to oxidation using Aldh, with reacts condensation. The most important are the condensation of acetaldehyde with biogenic amines and intervention of the product in exchange of catecholamines.
According to modern concepts, there are other ways catabolism of ethanol. It is established that originalie nucleotides accelerate the elimination of alcohol from the body. In acute alcohol intoxication alcohol is involved in the destruction of phosphate esters by hydrolytic mechanism. In addition, specific detected enzyme system, forming esters of ethanol with fatty acids in the liver cells, heart and, probably, in other tissues (Ostrovsky and others, 1986).
As already noted, the rate of oxidation of alcohol subject to large individual fluctuations. Partly it depends on circadian rhythms, and the levels of sex hormones, and volume of supply.