Enzymes bakers yeast

Very few enzyme-catalysed reactions involving the reduction of alkenes have achieved any degree of recognition in synthetic organic chemistry. Indeed the only transformation of note involves the reduction of a, (3-unsaturated aldehydes and ketones. For example, bakers yeast reduction of (Z)-2-bromo-3-phenylprop-2-enal yields (S)-2-bromo-3-phenylpropanol in practically quantitative yield (99 % ee) when a resin is employed to control substrate concen-tration[50]. Similarly (Z)-3-bromo-4-phenylbut-3-en-2-one yields 2(5), 3(,S)-3-bromo-4-phenylbutan-2-ol (80% yield, >95% ee)[51]. Carbon-carbon double bond reductases can be isolated one such enzyme from bakers yeast catalyses the reduction of enones of the type Ar—CH = C(CH3)—COCH3 to the corresponding (S)-ketones in almost quantitative yields and very high enantiomeric excesses[52]. 

Enzyme reductions of carbonyl groups have important applications in the synthesis of chiral compounds (as described in Chapter 10). Dehydrogenases are enzymes that catalyse, for example, the reduction of carbonyl groups they require co-factors as their co-substrates. Dehydrogenase-catalysed transformations on a practical scale can be performed with purified enzymes or with whole cells, which avoid the use of added expensive co-factors. Bakers yeast is the whole cell system most often used for the reduction of aldehydes and ketones. Biocatalytic activity can also be used to reduce carbon carbon double bonds. Since the enzymes for this reduction are not commercially available, the majority of these experiments were performed with bakers yeast1 41. 

Enzymes are natural biocatalysts that are becoming increasingly popular tools in synthetic organic chemistry [1]. The major areas of exploration have involved the use of hydrolases, particularly esterases and lipases [2]. These enzymes are readily available, robust and inexpensive. The second most popular area of investigation has been the reduction of carbonyl compounds to chiral secondary alcohols using either dehydrogenases (with co-factors) or a whole-cell system such as bakers yeast [3]. 

Cetylpyridinium chloride (CPC)/ hexane a-Amylase from brewers yeast and invertase from bakers yeast Enzyme activities in cells entrapped in RMs were high compared to free cells [284]... 

P. Dunnill, and M. D. Lilly, Release of enzymes from bakers yeast by disruption... 

The enantioselective synthesis of 2-phenylisoserine derivatives is an attractive goal and several attempts, such as the application of acylase (36), lipase [37], and, more recently, bakers yeast reductase enzymes [38], were made to prepare the taxol side chain (see Section 15.1). No nitrile-converting enzymes have been investigated so far. The chemical instability of 2-hydroxy-3-amino-3-phenylpropionitrile (a cyanohydrin) in aqueous solution afforded the preparation of the cyclic protection products tron.s-( )-8a and ds-( )-9a (Figure 15.2). 

This enzyme [also known at l(-[-)-lactate dehydrogenase] was first extracted from bakers yeast by Bernheim in 1928 (272). Bach et al. (273) showed in 1942 that lactate dehydrogenase copurified with a species of cytochrome b, which contained protoheme as prosthetic group. The... 

Connectivity theorems allow to relate the control coefficients (systemic properties) to the elasticity coefficients (properties of the network s enzymes individually as if in isolation) (Westerhoff and Van Dam 1987 Heinrich and Schuster 1996 Fell 1997). The connectivity theorems have given us a strong insight into the functioning of metabolic pathways. For example, it follows directly from these theorems that enzymes that are very sensitive to the concentrations of metabolites, such as substrates, products and allosteric effectors, tend to have little control over the flux. This is illustrated by overproduction of phosphofructokinase in bakers yeast, an enzyme often referred to textbooks as rate-limiting. Yet, overproduction of phosphofructokinase does not lead to a significant flux increase, since the cell compensates by lowering the level of its allosteric effector fructose 2,6-bisphosphate (Schaaff et al. 1989 Davies and Brindle 1992). 

The following experiment was conducted with a soluble starch in order to obtain solutions clear enough to permit determination of the optical activity. Reduction was determined with hypoiodite and calculated as degree of hydrolysis. Maltose and D-glucose were determined by fermentation with bakers yeast, Table II. The enzyme was quite... 

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]. 

Saccharomyces cerevisiae Bakers yeast—bread Brewers yeast—beer, wine, cider, etc. Enzyme (invertase) Gene expression system Dietary supplement... 

The problems encountered with the bakers yeast whole cell process may be overcome by the appUcation of isolated enzymes. Pohls group applied site-directed mutagenesis strategies to tailor PDC for fhe synfhesis of (P)-PAC. They... 

Reduced selectivity in bakers yeast mediated transformations is most likely due to the presence of several alcohol dehydrogenases possessing opposite enantioselectivity. Stewart et al. have successfully cloned 49 different oxidoreductases from Saccharomyces cerevisiae [47]. They could show that the identification of specific alcohol dehydrogenases will result in access to chiral alcohols in high optical purity. Moreover, both enantiomers are accessible sometimes using enzymes from one parental strain [48]. 

Separation of microorganisms and their fragments when processing fermentation products such as bakers yeast, single cell proteins, vaccines, amino acids and enzymes... 

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