The alcohol dehydrogenase system

At blood concentrations below 100 mg/dL (22 mmol/L), the MEOS system, which has a relatively high Km for alcohol, contributes little to the metabolism of ethanol. However, when large amounts of ethanol are consumed, the alcohol dehydrogenase system becomes saturated owing to depletion of the required cofactor, NAD+. As the concentration of... 

The effect of pH on oxidation-reduction potentials can be illustrated with the alcohol dehydrogenase system. Instead of pH 7.0, consider the reaction at pH 11.0. The acetaldehyde-ethanol couple will have an Eo of -0.200 - (4 X 0.06) = -0.440. The DPN-DPNH couple, involving only 1 hydrogen ion, changes from —0.320 to —0.440 volts. AE now is zero, and log IT, is zero. Ken, therefore, is 1. 

Formate dehydrogenase in conjunction with polyethyleneglycol-immobilized nicotinamide adenine dinudeotide has been used to good effect as a cofactor recycle system (39). The alcohol dehydrogenase from Thermoanaerobium hrockii catalyzed the reduction of ketones independently when driven by the cooxidation of isopropanol (40,41). 

In another approach, Yoneyama used electrogenerated and regenerated 1-phenyl-ethanol as reducing equivalent for the alcohol dehydrogenase-catalyzed regeneration of NADH. In this system, the production enzyme and the cofactor regenerating enzyme are identical. A production of 2 pmol was reached at turnover frequency of 1.7 TN/h or less (Fig. 9) [46]. 

The same system was applied to the HLADH catalyzed oxidation of a number of other meso-d o s, with similar results. Using the alcohol dehydrogenase from thermoanaer-obiuni brockii, it was possible to oxidize 2,4-pentanediol to give (5)-4-hydroxy-2-penta-none under indirect electrochemical regeneration of NADP". ... 

Over 90% of alcohol in the plasma is metabolized in the liver by three enzyme systems that operate within the hepatocyte. The remainder is excreted by the lungs and in urine and sweat. Alcohol is metabolized to acetaldehyde by alcohol dehydrogenase in the cell. In turn, acetaldehyde is metabolized to carbon dioxide and water by the enzyme aldehyde dehydrogenase. A second pathway for oxidation of alcohol uses catalase, an enzyme located in the peroxisomes and microsomes. The third enzyme system, the microsomal alcohol oxidase system, has a role in the oxidation of alcohol to acetaldehyde. These last two mechanisms are of lesser importance than the alcohol dehydrogenase-aldehyde dehydrogenase system. 

Two triple bioluminescent enzymatic systems were used with the alcohol dehydrogenase and trypsin. Activity of alcohol dehydrogenase and trypsin was determined by bioluminescent method from the decay constant of bioluminescence. ... 

Ethanol is metaboli/ed to acetaldehyde by two main pathways (Fig. 2). The alcohol dehydrogenase route is operational when the blood alcohol concentration is in the range 1-5 mmol/1. Above this most of the ethanol is metaboli/ed via the microsomal P450 system. Although the end product in both cases is acetaldehyde, the side effects of induced P450 can be significant. Ethanol metabolism and excretion in a nomial 70 kg man is summari/.ed in Figure 3. 

The alcohol dehydrogenase reaction occurs in the opposite direction when ethanol is consumed. Alcohol dehydrogenase is found in liver and intestinal tissue. The acetaldehyde produced by liver alcohol dehydrogenase may contribute to short- and long-term alcohol toxicity. Conversely, different levels of intestinal alcohol dehydrogenase may help explain why some individuals show more profound effects after only one or two drinks than others. Apparently, some of the ethanol consumed is metabolized by intestinal alcohol dehydrogenase before it reaches the nervous system. 

Fossati, E., et al.. Exploitation of the alcohol dehydrogenase-acetone NADP-regeneration system for the enzymatic preparative-scale production of 12-ketochenodeoxycholic acid. Biotechnol. Bioeng., 2006.93(6) 1216-1220. 

The reverse reaction also occurs m living systems NADH reduces acetaldehyde to ethanol m the presence of alcohol dehydrogenase In this process NADH serves as a hydride donor and is oxidized to NAD" while acetaldehyde is reduced... 

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