Alcohol biological oxidation

According to the proposed mechanism for biological oxidation of ethanol, the hydrogen that is transferred to the coenzyme comes from C-1 of ethanol. Therefore, the dihydropyridine ring will bear no deuterium atoms when CD3CH2OH is oxidized, because all the deuterium atoms of the alcohol are attached to C-2. 

Biological. Dodecane may biodegrade in two ways. The first is the formation of dodecyl hydroperoxide which decomposes to 1-dodecanol. The alcohol is oxidized forming dodecanoic acid. The other pathway involves dehydrogenation to 1-dodecene, which may react with water, giving 1-dodecanol (Dugan, 1972). 

Biological oxidation of methanol and ethanol in the body produces the corresponding aldehyde followed by the acid. At times the alcoholics, by mistake, drink ethanol, mixed with methanol also called denatured alcohol. In the body, methanol is oxidised first to methanal and then to methanoic acid, which may cause blindness and death. A methanol poisoned patient is treated by giving intravenous infusions of diluted ethanol. The enz5mie responsible for oxidation of aldehyde (HCHO) to acid is swamped allowing time for kidneys to excrete methanol. 

Alcohol dehydrogenases (ADH EC 1.1.1.1), for which several X-ray structures are available ", catalyze the biological oxidation of primary and secondary alcohols via the formal transfer of a hydride anion to the oxidized form of nicotinamide adenine dinucleotide (NAD ), coupled with the release of a proton. Liver alcohol dehydrogenase (LADH) consists of two similar subunits, each of which contains two zinc sites, but only one site within each subunit is catalytically active. The catalytic zinc is coordinated in a distorted tetrahedral manner to a histidine residue, two cysteine residues and a water molecule. The remaining zinc is coordinated tetrahedrally to four cysteine residues and plays only a structural role . 

The dehydrogenation of an alcohol to a ketone or aldehyde (Eq. 15-1) is one of the most frequent biological oxidation reactions. Although the hydrogen atoms removed from the substrate are often indicated simply as 2[H], it was recognized early in the twentieth century that they are actually transferred to hydrogen-carrying coenzymes such as NAD+, NADP+, FAD, and riboflavin... 

There are many biological oxidations that convert a primary or secondary alcohol to a carbonyl compound. These reactions cannot possibly involve the extreme pH conditions and vigorous inorganic oxidants used in typical laboratory oxidations. Rather, they occur at nearly neutral pH values and they all require enzymes as catalysts, which for these reactions usually are called dehydrogenases. 

Assumption of a similar metabolic change might clear up some aspects of the biological oxidation of toluene to benzoic acid. Bray, Thorpe and White131 have studied the kinetics of the oxidation of both benzyl alcohol and benzaldehyde to benzoic acid. The velocity constant for the oxidation of the alcohol is 1.0, and that for the aldehyde is only 0.3, indicating that both cannot be intermediates in the oxidation of toluene. Since the alcohol has already been shown to be an intermediate, it follows that the aldehyde is not. They pointed out that hydrate formation and D-glu-curonic conjugation may precede oxidation. 

Oxidation States of Alcohols and Related Functional Groups 467 11-2 Oxidation of Alcohols 469 11-3 Additional Methods for Oxidizing Alcohols 472 11-4 Biological Oxidation of Alcohols 474 11-5 Alcohols as Nucleophiles and Electrophiles Formation ofTosylates 476... 

NAD) A biological oxidizing/reducing reagent that operates in conjunction with enzymes such as alcohol dehydrogenase, (p. 474)... 

The following equation shows how NAD+ serves as the oxidizing agent in the biological oxidation of an alcohol. Just the nicotinamide portion of NAD shown takes part in the reaction. The enzyme that catalyzes this reaction is called alcohol dehydrogenase (ADH). 

Figure 17.8 The biological oxidation of an alcohol sn-glycerol 3-phosphate) to give a ketone (dihydroxy acetone phosphate). This mechanism is the exact opposite of the ketone reduction shown previously in Figure 17.4.

NAD% the oxidized form of NADH, is a biological oxidizing agent capable of oxidizing alcohols to carbonyl compounds (it forms NADH in the process). NAD is synthesized from the vitamin niacin, which can be obtained from soybeans among other dietary sources. Breakfast cereals are fortified with niacin to help people consume their recommended daily allowance of this B vitamin. 

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