5-selective alcohol dehydrogenase

The / e-face selective alcohol dehydrogenase from Curvularia falcata is not the only system capable of reducing cyclic and bicyclic ketones. The following reduction is observed with the fungus Aureohasidium pullulans28. 

The hand-in-glove fit of a chiral substrate into a chiral receptor is relatively straightforward, but it s less obvious how a prochiral substrate can undergo a selective reaction. Take the reaction of ethanol with NAD+ catalyzed by yeast alcohol dehydrogenase. As we saw at the end of Section 9.13, the reaction occurs with exclusive removal of the pro-R hydrogen from ethanol and with addition only to the Re face of the NAD+ carbon. 

Sachs, M.M. Freeling, M. (1978). Selective synthesis of alcohol dehydrogenase during anaerobictreatment of maize. Mo/ecw/ar andCcMera/Ccncrics, 161,111-15. 

An (5)-specific alcohol dehydrogenase gene from Rhodococcus erythropolis and GDH from Bacillus subtilis were ligated into one plasmid, which was expressed in Escherichia coli strain DSM14 459 to provide an (S)-selective whole-cell catalyst. 

Rhin(bpy)3]3+ and its derivatives are able to reduce selectively NAD+ to 1,4-NADH in aqueous buffer.48-50 It is likely that a rhodium-hydride intermediate, e.g., [Rhni(bpy)2(H20)(H)]2+, acts as a hydride transfer agent in this catalytic process. This system has been coupled internally to the enzymatic reduction of carbonyl compounds using an alcohol dehydrogenase (HLADH) as an NADH-dependent enzyme (Scheme 4). The [Rhin(bpy)3]3+ derivative containing 2,2 -bipyridine-5-sulfonic acid as ligand gave the best results in terms of turnover number (46 turnovers for the metal catalyst, 101 for the cofactor), but was handicapped by slow reaction kinetics, with a maximum of five turnovers per day.50... 

Because the direct electrochemical oxidation of NAD(P)H has to take place at an anode potential of + 900 mV vs NHE or more, only rather oxidation-stable substrates can be transformed without loss of selectivity—thus limiting the applicability of this method. The electron transfer between NADH and the anode may be accellerated by the use of a mediator. At the same time, electrode fouling which is often observed in the anodic oxidation of NADH can be prevented. Synthetic applications have been described for the oxidation of 2-hexene-l-ol and 2-butanol to 2-hexenal and 2-butanone catalyzed by yeast alcohol dehydrogenase (YADH) and the alcohol dehydrogenase from Thermoanaerobium brockii (TBADH) repectively with indirect electrochemical... 

In the case of horse liver alcohol dehydrogenase, a homodimeric enzyme, Subramanian et al.(202) used the relative phosphorescence of tyrosine and tryptophan to examine the effects of various ternary complexes known to selectively quench the fluorescence of the tryptophans of each subunit. One proposed quenching mechanism is the formation of a ground-state tyrosinate in a ternary complex at neutral pH.(201) This tyrosinate, by being a resonance... 

In protein molecules with two or more tryptophan residues, it is necessary to obtain first the fluorescence decay curves for the individual residues. For this purpose, additional spectroscopic information is necessary. One can use the dependence of the decay curves on emission wavelength, apply selective fluorescence quenchers, or selectively modify one of the tryptophan residues. The results of Brochon et al. for the lac repressor(44) and those of Beechem et al. for alcohol dehydrogenase(45) provide evidence in favor of such approaches. 

A somewhat different approach to determining the enantiopurity of a sample is based on the idea that an appropriate enzyme selectively processes one enantiomer, giving rise to a UV/visible signal [17]. An example concerns determination of the enantiopurity of chiral secondary alcohols, the (S) enantiomer being oxidized selectively by the alcohol dehydrogenase from Thermoanaerobium sp. The rate of this process can be monitored by a UV/visible plate reader due to the formation of NADPH (absorption at 340 nm), which relates to the quantity of the (S) enandomer present in the mixture. About 4800 ee determinadons are possible per day, accuracy amoundng to 10%. Although the screen was not specifically developed to evaluate chiral alcohols produced by an enzymadc process, it is conceivable that this could be possible after an appropriate extraction process. 

Soon after the initial discovery, it became apparent that neither the source of the enzyme, nor the type of enzyme, nor the type of solvent seem to constrain the use of organic solvents (Zaks, 1986a). Various types of enzymes, such as lipases, proteases (chymotrypsin, subtilisin), oxidoreductases (alcohol dehydrogenase, oxidases, and peroxidases), and others, react in organic solvents. A selection of enzymes... 

Chiral alcohols are valuable products mainly as building blocks for pharmaceuticals or agro chemicals or as part of chiral catalysts. Cheap biotransformation methods for the selective reduction of particular ketone compounds are known for many years rather catalyzed by fermentation than with isolated enzymes. Products prepared with whole cells such as baker s yeast often lack high enantioselectivity and there were several attemps to use isolated enzymes. Resolution of racemates with hydrolases are known in some cases but very often the reduction of the prochiral ketone using alcohol dehydrogenases are much more attractive. 

The biochemical characterization of several alcohol dehydrogenases and their exploitation potential demonstrate that these enzymes are most important tools for biochemists. Amino acid sequences of several ADFls are available so far, and alignment studies allow to establish ADH families and to consider their probable evolutionary relationships. For preparative applications, however, particular properties of an enzyme are essential prerequisites, such as enzyme stability and availability, its substrate specificity, or reaction selectivity. Enzymes with NAD as coenzyme are clearly preferred to NADP-dependent ones in practice, because NAD has a significantly higher stability [186-188], a lower price and, is in general, easier to regenerate. 

When simulating the alcohol dehydrogenase, the investigators met with economic problems because the NAD+ co-factor is very expensive. Therefore, several methods of its regeneration were developed, among which the most effective method is non-enzymatic continuous regeneration of catalytic amounts of NADHL and NAD+ with sodium dithionite [127], This method can be used for HLADH synthesis, used in the catalytic reduction of a wide selection of aldehydes and ketones. 

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