Metabolic ethanol

Our bodies are reasonably well equipped to metabolize ethanol making it less dan gerous than methanol Alcohol abuse and alcoholism however have been and remain persistent problems... 

Alcohol dehydrogenase is present in many organisms that metabolize ethanol, including humans. In human liver it catalyzes the oxidation of ethanol, either ingested or produced by intestinal microorganisms, with the concomitant reduction of NAD+ to NADH. 

Metabolically, ethanol is oxidized first to acetaldehyde (Section 14.6), then to C02. The overall oxidation rate is faster than that for methanol. 

Important characteristics of zero-order reactions are that (1) a constant amount of drug is eliminated per unit time since the system is saturated (maximized) and (2) the half-life is not constant for zero-order reactions but depends on the concentration. The higher the concentration, the longer the half-life. Therefore, the term zero-order half-life has little practical significance since it can change and (3) zero-order kinetics is also known as nonlinear or dose-dependent. For example, if the body can metabolize ethanol at a rate of 10 ml per hour, then if one consumes 60 ml, it will take 3 hours to metabolize half of it (the half-life under these circumstances). However, if 80 ml is consumed the half-life will now become 4 hours. This is particularly significant regarding ethanol toxicity. 

All of them are product and process dependent but generally an increased yield of product on the substrate [128] and an increased growth rate are common properties that S. cerevisiae is required to have in order to produce an efficient processes. More specific desired features are the high productivity of ethanol in brewing and wine making, of CO2 in baking, and minimization of overflow metabolism (ethanol and glycerol) and increased biomass yield on the substrate in applications where product formation is directly coupled to biomass. 

Inhibiting methanol metabolism. Ethanol, which occupies the dehydrogenase enzymes in preference to methanol, competitively prevents metabolism of methanol to its toxic products. A single oral dose of ethanol 1 ml/kg (as a 50% solution or as the equivalent in gin or whisky) is followed by 0.25 ml/kg/h orally or i.v., aiming to maintain the blood ethanol at about... 

Aldehyde dehydrogenase Fast, slow metabolizers Ethanol Slow facial flushing Fast protection from liver cirrhosis... 

The for this catalase and for the mixed-function oxidase is about 10 mM/L. The extent to which these two enzymes metabolize ethanol is not known. 

The adverse effects of ethanol are not limited to the metabolism of ethanol itself. Vitamin A (retinol) is converted into retinoic acid, an important signal molecule for growth and development in vertebrates, by the same dehydrogenases that metabolize ethanol. Consequently, this activation does not take place in the presence of ethanol, which acts as a competitive inhibitor. Moreover, the MEOS system induced by ethanol inactivates retinoic acid. These disruptions in the retinoic acid signaling pathway are believed to be responsible, at least in part, for fetal alcohol syndrome as well as the development of a variety of cancers. 

Although the major metabolic pathway for ethanol is via alcohol dehydrogenase (see below) there is also a microsomal ethanol oxidizing system (MEOS) which metabolizes ethanol to ethanal. The mechanism may involve hydroxylation at the carbon atom, although this is uncertain. Although this enzyme system is of minor importance in naive subjects, exposure to ethanol can induce the enzyme system such that it becomes the major enzyme system metabolizing ethanol. 

The treatment of methanol poisoning involves firstly the administration of an antidote, ethanol, which blocks metabolism. Ethanol competes with methanol for alcohol dehydrogenase as the enzyme has a greater affinity for ethanol. Methanol metabolism can be reduced by as much as 90% by an equimolar dose of ethanol and the half-life becomes extended to 46 h. 4-Methylpyrazole, which also binds to alcohol dehydrogenase, has been used successfully in monkeys to treat methanol poisoning, as has folic acid. 

Ethanol has countless applications as a solvent for organic chemicals and as a starting compound for the manufacture of dyes, synthetic drugs, cosmetics, and explosives. It is also a constituent of alcoholic beverages. Ethanol is the only nontoxic (more properly, the least toxic) of the straight-chain alcohols our bodies produce an enzyme, called alcohol dehydrogenase, which helps metabolize ethanol by oxidizing it to acetaldehyde ... 

Methanol and ethylene glycol (antifreeze) are both metabolized by tilcohol dehydrogena.se to formic and oxalic acids, which are toxic. In order to prevent this metabolism, ethanol is infused to a concentration of 20 mmol/l until the alcohols, methanol and ethylene glycol, are excreted unchanged. Alcoholics w ho drink ethanol as well as methanol in fact protect themselves against the worst effects of methanol poisoning. 

Pharmacokinetics After ingestion, ethanol is rapidly and completely absorbed the drug is then distributed to most body tissues, and its volume of distribution is equivalent to that of total body water (0.5-0.7 L/kg). Two enzyme systems metabolize ethanol to acetaldehyde (Figure 23-1). 

Welch, P. and Scopes, R.K. (1985) Studies on cell-free metabolism ethanol production by a yeast glycolytic system... 

The rate of ethanol production by Mucor was lower when high concentrations of D-xylose (200 gl ) were used as substrates, indicating that Mucor is more sensitive to high concentration of D-xylose than Fusarium [13]. At low substrate concentration, reduced yield of ethanol by Fusarium F5 was observed after 4 days of incubation, thus, indicating the ability of Fusarium to utilise ethanol upon the exhaustion of D-xylose [13]. Similar results were obtained with F. oxysporum VTT-D-80134 where sugars were found to be consumed in 2 days and then the organism utilized the ethanol produced previously [33]. Some of the fungal cultures have also been reported which metabolize ethanol into acetic acid [76, 85]. 

Persons who chronically overuse alcohol would develop another enzyme system in the fiver that metabolizes ethanol. The enzyme is dependent on cytochrome P-450, and is called CYP2E1. (Please refer to Chapter 6 for a brief discussion of cytochrome P-450). 

S. cerevisiae can metabolize ethanol by the respiratory pathway in the presence of small quantities of glucose. After alcoholic fermentation, oxidative yeasts develop in a similar manner on the surface of wine as part of the process of making certain specialty wines (Sherry, Yellow Wine of Jura). 

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