Alcohol dehydrogenase reaction catalyzed

Alcohol dehydrogenases catalyze oxidation of alcohols in a reaction dependent on the pyridine nucleotide NAD+ [Eq. (5)]. Since the reaction is reversible, alcohol dehydrogenases also catalyze the reduction of aldehydes by... 

Klinman, J.P. (1976). Isotope effects and structure-reactivity correlations in the yeast alcohol dehydrogenase reaction. A study of the enzyme-catalyzed oxidation of aromatic alcohols. Biochemistry 15, 2018-2026... 

This enzyme [EC 1.1.99.8], also known as alcohol dehydrogenase (acceptor), catalyzes the reaction of a primary alcohol with an acceptor to produce an aldehyde and the reduced acceptor. A wide range of primary alcohols (c.g., methanol) can serve as substrates. 

Horse liver alcohol dehydrogenase (LADH) catalyzes the reactions of aldehydes and their corresponding alcohols with the coenzymes NADH and NAD+. Activation of substrate complexes via polarization of substrate C=0 bond has been observed in LADH by vibrational spectroscopy. Two enzyme complexes have been studied by difference Raman measurements, the E/NADH DABA complex [17, 18] and the E/NADH CXF complex [19]. DABA is a poor substrate while CXF is a substrate analog. X-ray crystallography has shown that the polarization of the substrate C=0 bond is mainly due to a coordination to the active site Zn++ ion [20, 21]. For example, polarization of the C=0 bond of DABA in the LADH complex was found to be substantial, half way between a single and double bond as compared to DABA in solution [18]. 

Comparisons of the kinetic coefficients in Eq. (1) obtained from initial rate measurements with alternative substrates have given a considerable amount of information about reaction pathways as well as indications of the molecular basis of specificity (60). This approach, much used for proteolytic enzymes, has been exploited particularly with the alcohol dehydrogenases, which catalyze the oxidation of a variety of primary and secondary alcohols (61). While several other dehydrogenases have been studied in this way, most of the results have been reported only as apparent maximum rates and apparent Km values for the alternative substrate, which restricts the amount of information that can be derived. 

There are several classes of alcohol dehydrogenases that catalyze the reversible oxidation/reduction reaction of alcohols to aldehydes (Testa and Kramer, 2007 ... 

Only in the case of alcohol dehydrogenase (ADH)-catalyzed reactions, a substrate-coupled system can be applied, in which the enzyme that transforms the substrate of interest also regenerates the cofactor at the expense of a co-substrate to be used in at least stoichiometric amounts with respect to the substrate. 

In human liver cells, the enzyme alcohol dehydrogenase (LADH) catalyzes the oxidation of ethanol to yield acetaldehyde. In this reaction, the coenzyme nicotinamide adenine dinucleotide, NAD, is converted to its reduced form, NADH. 

Imidazohum-based ILs were used as nonconventional media in alcohol dehydrogenase (ADH)-catalyzed reactions in enzymatic catalysis. When containing up to 50% of the IL, the overall conversion could be improved in some cases, while the stereoselectivity of the enzyme remained unaltered. 

Although alcohol dehydrogenases (ADH) also catalyze the oxidation of aldehydes to the corresponding acids, the rate of this reaction is significantly lower. The systems that combine ADH and aldehyde dehydrogenases (EC 1.2.1.5) (AldDH) are much more efficient. For example, HLAD catalyzes the enantioselective oxidation of a number of racemic 1,2-diols to L-a-hydroxy aldehydes which are further converted to L-a-hydroxy acids by AldDH (166). 

ATP D-frnctose-6-phosphate 1-phosphotrans-ferase, and alcohol dehydrogenase (ADH), or alcohol NAD oxidoreduetase, which catalyze the reactions shown here. 

As another example, studies with deuterium-labeled substrates have shown that the reaction of ethanol with the coenzyme NAD+ catalyzed by yeast alcohol dehydrogenase occurs with exclusive removal of the pro-R hydrogen from ethanol and with addition only to the Re face of NAD+. 

Step 3 of Figure 29.3 Alcohol Oxidation The /3-hydroxyacyl CoA from step 2 is oxidized to a /3-ketoacyl CoA in a reaction catalyzed by one of a family of L-3-hydroxyacyl-CoA dehydrogenases, which differ in substrate specificity according to the chain length of the acyl group. As in the oxidation of sn-glycerol 3-phosphate to dihydroxyacetone phosphate mentioned at the end of Section 29.2, this alcohol oxidation requires NAD+ as a coenzyme and yields reduced NADH/H+ as by-product. Deprotonation of the hydroxyl group is carried out by a histidine residue at the active site. 

Formally, in redox reactions there is transfer of electrons from a donor (the reductant) to the acceptor (the oxidant), forming a redox couple or pair. Oxidations in biological systems are often reactions in which hydrogen is removed from a compound or in which oxygen is added to a compound. An example is the oxidation of ethanol to acetaldehyde and then to acetic acid where the oxidant is NAD. catalyzed by alcohol dehydrogenase and acetaldehyde dehydrogenase, respectively. 

Future directions in alcohol dehydrogenase-catalyzed reactions... 

Figure 17.19 A membianeless ethanol/02 enz3fme fuel cell. Alcohol dehydrogenase and aldehyde dehydrogenase catalyze a stepwise oxidation of ethanol to acetaldehyde and then to acetate, passing electrons to the anode via the mediator NAD+/NADH. At the carhon cathode, electrons are passed via the [Ru(2,2 -bipyridyl)3] and biUverdin/bilimbin couples to bilirubin oxidase, which catalyzes O2 reduction to H2O. (a) Schematic representation of the reactions occruring. (b) Power/cmrent response for the ceU operating in buffered solution at pH 7.15, containing 1 mM ethanol and 1 mM NAD. Panel (b) reprinted from Topcagic and Minteer [2006]. Copyright Elsevier, 2006.

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