Organic biocatalysis

Ishige, T., Honda, K., and Shimizu, S. 2005. Whole organism biocatalysis. Curr. Op. Chem. Biol, 9(2), 174-180. 

Successful acceleration by sonication has also been reported in the field of organic biocatalysis, employing whole cell and immobilized enzymes. The improved yields and retained stereoselectivities obtained under ultrasound irradiation emphasize the broad range of chemical transformations that benefits from ultrasonic treatment. 

Ishige T, Honda K, Shimizu S. Whole organism biocatalysis. Current Opinion in Chemical Biology 9(2), 174, 2005. 

Biocatalysis Chemical reactions mediated by biological systems (microbial communities, whole organisms or cells, cell-free extracts, or purified enzymes aka catalytic proteins). 

C. Veeger, in Biocatalysis in organic media (C. Laane, J. Tramper, M. D. Lilly eds.), Elsevier, Amsterdam, 1987. P. Bonhote, A. P. Dias, K. Papageor-eiou, M. Gratzel, Inorg. Chem. 1996,... 

Before discussing the medium engineering phenomenon and its synthetic relevance in details, it is useful to offer a brief overview of the fundamentals of biocatalysis in organic media. 

In the last decade, biocatalysis in nonaqueous media, using hydrolases, has been widely used for organic chemists. The possibilities that these biocatalysts offer for the preparation of different types of organic compounds, depending upon the nucleophile... 

In this volume not all stress types are treated. Various aspects have been reviewed recently by various authors e.g. The effects of oxygen on recombinant protein expression by Konz et al. [2]. The Mechanisms by which bacterial cells respond to pH was considered in a Symposium in 1999 [3] and solvent effects were reviewed by de Bont in the article Solvent-tolerant bacteria in biocatalysis [4]. Therefore, these aspects are not considered in this volume. Influence of fluid dynamical stresses on micro-organism, animal and plant cells are in center of interest in this volume. In chapter 2, H.-J. Henzler discusses the quantitative evaluation of fluid dynamical stresses in various type of reactors with different methods based on investigations performed on laboratory an pilot plant scales. S. S. Yim and A. Shamlou give a general review on the effects of fluid dynamical and mechanical stresses on micro-organisms and bio-polymers in chapter 3. G. Ketzmer describes the effects of shear stress on adherent cells in chapter 4. Finally, in chapter 5, P. Kieran considers the influence of stress on plant cells. 

Biocatalysis refers to catalysis by enzymes. The enzyme may be introduced into the reaction in a purified isolated form or as a whole-cell micro-organism. Enzymes are highly complex proteins, typically made up of 100 to 400 amino acid units. The catalytic properties of an enzyme depend on the actual sequence of amino acids, which also determines its three-dimensional structure. In this respect the location of cysteine groups is particularly important since these form stable disulfide linkages, which hold the structure in place. This three-dimensional structure, whilst not directly involved in the catalysis, plays an important role by holding the active site or sites on the enzyme in the correct orientation to act as a catalyst. Some important aspects of enzyme catalysis, relevant to green chemistry, are summarized in Table 4.3. 

The use of ionic liquids (ILs) to replace organic or aqueous solvents in biocatalysis processes has recently gained much attention and great progress has been accomplished in this area lipase-catalyzed reactions in an IL solvent system have now been established and several examples of biotransformation in this novel reaction medium have also been reported. Recent developments in the application of ILs as solvents in enzymatic reactions are reviewed. 

Important topics in biocatalysis for organic synthesis are described in this book, for experts and non-experts. Especially, the book focuses on those reactions that are under development now and will be more significant in the future. Therefore, each chapter describing a specific theme summarizes not only the present state but also the direction of the research. The prospects and dreams that will become possible, using biocatalysis, in the future to construct a sustainable society are also included. 

Boundary membranes play a key role in the cells of all contemporary organisms, and simple models of membrane function are therefore of considerable interest. The interface of two immiscible liquids has been widely used for this purpose. For example, the fundamental processes of photosynthesis, biocatalysis, membrane fusion and interactions of cells, ion pumping, and electron transport have all been investigated in such interfacial systems. 

The use of organic solvent in the medium is one stategy that has been proposed for biocatalysis [9-15]. In the organic phase, the reactant has a much greater solubility than in the aqueous phase. This could significantly reduce the volume of the reaction mixture. Enzymes and micro-organisms have been shown to be active in the presence of organic solvents [16-20]. 

The present review deals with the same topic as the articles cited above, but modified with different parameters influencing biocatalysis and reactant partition in water-organic two-liquid phase bioreactors. Interactions between these phenomena are also discussed. 

Many studies have demonstrated that enzymes in organic media keep their conventional Michaelis-Menten or ping-pong behavior [10,132,133,137]. Nevertheless, enzyme activity usually decreases and kinetic parameters are dramatically changed when compared to biocatalysis in aqueous media [136]. 

The protein-containing colloidal solutions of water-in-organic solvents are optically transparent. Hence, absorption spectroscopy, circular dichroism spectroscopy and fluorescence spectroscopy are found to be convenient for studying biocatalysis [53]. The reversed micelles are interesting models for studying bioconversion, since the majority of the enzymes in vivo act inside or on the surface of biological membranes. 

A common characteristic of metabolic pathways is that the product of one enzyme in sequence is the substrate for the next enzyme and so forth. In vivo, biocatalysis takes place in compartmentalized cellular structure as highly organized particle and membrane systems. This allows control of enzyme-catalyzed reactions. Several multienzyme systems have been studied by many researchers. They consist essentially of membrane- [104] and matrix- [105,106] bound enzymes or coupled enzymes in low water media [107]. 

The present section deals with the improvement in the performance of biocatalysis when carried out in organic-aqueous biphasic systems. Such systems are very useful in equilibrium reactions and conversion yield where substrates and products can be dissolved and drawn into different phases. Subsequently the synthesis in the reactive aqueous phase is allowed to continue. 

As proven in this review and other papers, organic-aqueous biphasic media have been useful in many areas of biocatalysis applications. We summarize the potential advantages in carrying out biocatalysis in biphasic systems ... 

C. Laane, S. Boeren, R. Hilhorst, and C. Veeger, in Biocatalysis in Organic Media (C. Laane,... 

Vazquez-Duhalt, R. Fedorak, P. M., and Westlake, D. W. S., Role of Enzyme Hydrophobicity in Biocatalysis in Organic-Solvents. Enzyme and Microbial Technology, 1992. 14(10) pp. 837-841. 

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