Enzymatic reduction yeast

As mentioned above, Met(0) must be converted to Met before it can be incorporated into proteins. There are a wide variety of organisms that have been shown to be capable of enzymatically reducing Met(O) residues. The enzymatic reduction of free Met(O) to Met has been observed in yeast , E. cofi - , Pseudomonas , plants and animal tissues . The enzyme from E. coli has been purified about 1100-fold using a newly developed very sensitive assay . The assay involves first the conversion of [ S]Met(0) to [ S]Met by the Met(O) reductase followed by the measurement of [ S]Met-tRNA after enzymatic acylation of tRNA. Since Met(O) is not a substrate for the acylation reaction , the amount of [ S]Met-tRNA formed is proportional to the amount of [ S]Met(0) converted to [ S]Met. The assay is sensitive to Met levels of less than 1 pmol. 

S -tridecylacetate and 2S-tridec-1OE -enylacetate, the sex ph eromones of the fruit fly Drosophilia mulleri) and the Hessian fly Mayetiola destructor) have been synthesized using ethyl-SS-hydroxybutanoate, a product from the enzymatic reduction of ethyl acetoacetate by the soil yeast strain 80-l .l58... 

The enzymatic reduction of a thiocarbonyl compound has been investigated [159] for the first time, in order to provide a new route for enan-tiopure thiols, molecules which are currently needed for asymmetric synthesis. Reaction of easily available /1-thioxoesters with baker s yeast under classical conditions did furnish the expected thiols, but with lower enantiomeric purity and moderate conversion rate, due to the competitive hydrolysis of the thioxo group into a carbonyl leading to an alcohol. However, conditions (ethyl acrylate, dry yeast) were found to improve the production of (S)-ethyl 3-mercaptobutanoate. Cyclic thioxo esters led to high stereoselectivity of cis (1S,2S) products, but with moderate chemical yields. 

Diols may be prepared by reduction of a-diketones or a-hydroxy ketones such as biacetyl, benzoin, and benzil. Substituted benzoins containing methoxyl and p-dimethylamino groups have been reduced catalytically over platinum oxide and by sodium amalgam and alcohol. Levorotatory propylene glycol is made from acetol, CHjCOCHjOH, by an enzymatic reduction with yeast. ... 

Reduction of Aldehydes. Stereospecificially labeled primary alcohols are useful in biochemical and physical organic studies. Such compounds may be prepared by enzymatic reduction of a labeled aldehyde using yeast. However, isolation of the product is often tedious. Alpine-Borane greatly simplifies the process and provides compounds of high enantiomeric purity. It is the most efficient reagent available for reduction of aldehydes. The limiting... 

Baker s yeast reduces conjugated nitro compounds to nitroalkanes and also the C=C unit of conjugated ketones. Other enzymatic reductions are possible. A reductase from Nicotiana tabacum reduced a conjugated ketone to the saturated ketone, with excellent enantioselectivity. Enzyme YNAR-I and NADP-H reduces conjugated nitro compounds to nitroalkanes. ... 

In a different approach, instead of using a production enzyme together with an NADH-regenerating enzyme, baker s yeast was used to take over both objectives. Thus 3-keto esters were electrochemically reduced to give the optically active 3-hydroxy esters in the presence of baker s yeast and NAD" " using a viologen as redox catalyst to shuttle the electrons from the cathode to the yeast cells which then catalyze the NADH formation and the enzymatic reduction. In such an approach, usually the permeation in and out of the yeast cells is a limiting factor [54]. 

The thioredoxin system, consisting of thioredoxin and thioredoxin reductase, was originally discovered as the hydrogen carrier system, which provides, with NADPH, the reducing potential for the reduction of ribonucleotides (5, 35). Since then considerable evidence has been accumulated to indicate that this or a closely related system also participates in a variety of other enzymatic reductions. For instance thioredoxin can function as an electron carrier between NADPH and several disulfides, such as insulin, lipoate and oxidized glutathione. Furthermore Porque et al. (114) have shown that thioredoxin and thioredoxin reductase from yeast can function as hydrogen carriers in the reduction of methionine sulfoxide and sulfate. 

Enzymatic reductions are commonly used in asymmetrical synthesis (see Chap. 10). One of the most common methods uses baker s yeast (S. cerevisiae). The complete... 

The selective enzymatic reduction of 2-substituted / -keto esters or /S-diketones is more interesting than that of unsubstituted compounds since two stereogenic centers can be introduced into the molecule in one step. The observation that baker s yeast reduction of these compounds results in predominantly one of the four possible diastereomeric products has been explained by a keto- enol equilibration of the enantiomeric / -dicarbonyls with the simultaneous removal of one of these substrates by an asymmetric reduction49. 

Another enzymatic approach to obtain the desired stereochemistry in the side chain is shown in Scheme 17.13. The keto ester precursor 10 of the side chain ethyl ester can be reduced to the hydroxy (2R,3S) ester 11 using either of the yeasts Hansenula polymorpha SC 13865 or Hansemla fabianii SC 13894. Screening a variety of strains from our culture collection revealed many other strains that could carry out the reduction reaction, but the best yields and ee s using whole cells were obtained with the two strains of Hansenula. Of four possible reduction products, the desired product 11 is obtained with 95 to 99% ee and 80 to 90% yield. Because of rapid ketone/enol tautomerism, the enzymatic reduction can work as a dynamic resolution and fix the stereochemistry at both the 2- and 3-positions. 

Beer, on the other hand, is produced by more complex biochemical and technological processes, which all affect its flavor. Yeast amino acid metabolism, a key to the development of beer flavor as described earlier, is affected by process temperature and use of cell immobilization techniqnes. Therefore, technologies based on these features as well as other process conditions and strain selection have been developed to control beer flavor. The combination of immobilized yeast and low-temperature primary fermentation was found to produce beers with low diacetyl amounts, therefore indicating potential of low-cost industrial application since maturation is a high-energy-consuming process. Finally, Perpete and Collin showed that during alcohol-free beer production, the enzymatic reduction of worty flavor (caused by Strecker aldehydes) by brewer s yeast was improved by cold contact fermentation. 

Christen M, Crout DHG (1987) Enzymatic reduction of P-ketoesters using unmobilized yeast. In Moody GW, Baker PB (eds) Bioreactors and Biotransformatimts. Elsevier, London,p 213... 

The thioredoxins appear to have a highly specific relationship with the enzyme carrying out ttieir reduction. Yeast thioredoxin for example is not reduced by the thioredoxin reductase from E. coli. In contrast reduced thioredoxins may donate electrons to a variety of acceptors. Reduced thioredoxin is a good general disulphide reductant. In combination with its reductase a disulphide reductase system is formed which is capable of reducing lipoic acid, oxidized glutathione and other similar structures. In these cases the thioredoxin-disulphide redox system does not appear to require additional enzymatic components. 

The keto group of methyl acetoacetate may also be reduced selectively with sodium borohydride. Describe how the product of this reaction would differ from the product of the enzymatic reduction of methyl acetoacetate with baker s yeast. 

The NMR spectrum in Figure 17.21 is of a mixture of the chiral shift reagent 17 and a sample of methyl (S)-(+)-3-hydroxybutanoate that was produced by the enzymatic reduction of methyl acetoacetate using baker s yeast. Determine the enantiomeric excess of the methyl (S)-(+)-3-hydroxybutanoate contained in this sample. 

Black and Wright (J. Am. Chem. Soc. 76, 2271, 6766 (1953)), have now demonstrated the enzymatic formation of /3-aspartyl phosphate from n-aspartate and ATP and its enzymatic reduction to homoserine by a TPN-dependent enzyme system obtained from yeast. 

Enzymatic reduction is not limited to P-ketoesters and acids baker s yeast reduces a number of a-ketoacids with good chemical yield and enantioselectivity. 

The enzymatic reduction of a nonpolar substrate such as 2-heptanone to 5-2-heptanol catalyzed by yeast alcohol dehydrogenase in w/o microemulsions... 

Scheme 3.29 Additives in the enzymatic reduction with bakers yeast.

The first task was to prepare the chiral sulfoxide. The synthesis began with the conversion of methyl propionate (144) to keto-sulfide 145. Enzymatic reduction of the ketone using Baker s Yeast gave 146 with decent enantiose-lectivity. A directed oxidation of the sulfide provided an unequal mixture of sulfoxides 147 and 148 (and presumably minor amounts of material derived from the 4-5% of ent- 46 present in the starting material) from which 148 could be isolated in 50% yield. Dehydration of the alcohol provided 149 (along with some of the Z isomer). Notice that Mori decided to place the alcohol beta to the sulfoxide in the precursor of 149. There might be a number of reasons for this, but one is that it facilitated the elimination reaction (dehydration) because of the electron-withdrawing properties of the sulfoxide. 

Soluble organic solvents have often been used as cosolvents to solubilize miscible organic substrates. Since organic compounds including solvents are possibly incorporated inside of the enzyme, they may affect the stereoselectivity of enzymatic reactions. For example, dimethyl sulfoxide (DMSO) (10%) enhance not only chemical yield but also enantioselectivity of yeast reduction. Thus, the poor yield of 23% with 80% ee was increased to 65% yield with >99% ee (Figure 8.20) [17]. 

An IL solvent system is applicable to not only lipase but also other enzymes, though examples are still limited for hpase-catalyzed reaction in a pure IL solvent. But several types of enzymatic reaction or microhe-mediated reaction have been reported in a mixed solvent of IL with water. Howarth reported Baker s yeast reduction of a ketone in a mixed solvent of [hmim] [PFg] with water (10 1) (Fig. 16). Enhanced enantioselectivity was obtained compared to the reaction in a buffer solution, while the chemical yield dropped. 

The yeast-mediated enzymatic biodegradation of azo dyes can be accomplished either by reductive reactions or by oxidative reactions. In general, reductive reactions led to cleavage of azo dyes into aromatic amines, which are further mineralized by yeasts. Enzymes putatively involved in this process are NADH-dependent reductases [24] and an azoreductase [16], which is dependent on the extracellular activity of a component of the plasma membrane redox system, identified as a ferric reductase [19]. Recently, significant increase in the activities of NADH-dependent reductase and azoreductase was observed in the cells of Trichosporon beigelii obtained at the end of the decolorization process [25]. 

It is worth noting that finding a secondary a-deuterium KIE larger than the EIE is not unique. In fact, it has been found in several other reactions. For instance, Cleland and co-workers (Cook et al., 1980,1981 Cook and Cleland, 1981a,b) found unexpectedly large secondary a-deuterium KIEs in some enzymatic reactions for example, a secondary a-deuterium KIE of 1.22 for the reduction of acetone catalysed by yeast alcohol dehydrogenase and a KIE of 1.34 for the reduction of cyclohexanone catalysed by horse-liver dehydrogenase. 

A systematic study on enzymatic catalysis has revealed that isolated enzymes, from baker s yeast or old yellow enzyme (OYE) termed nitroalkene reductase, can efficiently catalyze the NADPH-linked reduction of nitroalkenes. Eor the OYE-catalyzed reduction of nitrocyclohexene, a catalytic mechanism was proposed in which the nitrocyclohexene is activated by nitro-oxygen hydrogen bonds to the enzymes His-191 and Asn-194 [167, 168]. Inspired by this study Schreiner et al. 

A patented process for the production of green notes applying bakers yeast for in situ reduction of enzymatically produced aldehydes [67, 68] has been called into question regarding the effective production of (Z)-3-hexenol. According to Gatfield s report [69] the isomerisation of (Z)-3-hexenol to (E)-2-hexenal is a very fast process. The latter undergoes facile conversion to hexanol. Beside this, baker s yeast can add activated acetaldehyde to ( )-2-hexenal, forming 4-octen-2,3-diol. 

Yeast-mediated reductions predominantly form a single enantiomer and it is often difficult to find conditions which produce the opposite stereoisomer selectively. It has, however, been possible to obtain both enantiomers in 50% yield in 100% via enzymatic optical resolution. Chiral fluorinated secondary alcohols possessing the mono-, di- and/or trifluoromethyl group have been prepared by enzyme-catalyzed kinetic resolutions [27]. 

---