Enzyme reactions, multi-step

The use of this enzyme in multi-step synthesis is relatively recent. Clapes et al. have reported the first example of FSA-mediated synthesis of iminocyclitols [53]. The synthetic strategy is similar to the one previously described for DHAP-dependent aldolases without the need for the dephosphorylation step. AldoUc reaction of DHA with N-Cbz-3-aminopropanal catalyzed by FSA followed by selective catalytic reductive aminahon furnishes the naturally occurring imino-sugar D-fagomine (Scheme 4.22). 

Heterogeneous catalysis One-step reactions Simple product recovery Enzyme engineering multi-step reactions no cofactor problems long catalyst lifetime metabolic engineering ... 

The H2-based reversibility of biological reactions occurs at levels ranging from individual enzymes to multi-step processes comprising a complete, dissim-ilatory metabohsm. The simplest example is the reversibility of hydrogenase enzymes themselves. A significant fraction of these enzymes can be made to either produce H2 while oxidizing a biological electron carrier, or to reduce a... 

Many other multisubstrate examples abound in metabolism. In effect, these situations are managed by realizing that the interaction of the enzyme with its many substrates can be treated as a series of uni- or bisubstrate steps in a multi-step reaction pathway. Thus, the complex mechanism of a multisubstrate reaction is resolved into a sequence of steps, each of which obeys the single- and double-displacement patterns just discussed. 

In the present paper we describe the catalytic mechanisms of synthetic polymer-Cu complexes a catalytic interaction between the metal ions which attached to a polymer chain at high concentration and an environmental effect of polymer surrounding Cu ions. In the latter half, the catalytic behavior is compared with the specific one of tyrosinase enzyme in the melanin-formation reaction which is a multi-step reaction. To the following polymers Cu ions are combined. 

Industrial and applied multi-step reaction processes, where oxidizing enzymes are components of industrial processes, include in the pulp and paper industry, in the food and beverage industry, for bioremediation, in biosensors and, more recently, in biofuel cells (discussed in more detail in Section 3.8). 

The main group of aldolases from the biocatalytic point of view is, arguably, the one that uses dihydroxyacetone phosphate (DHAP) as donor. Here, we will concentrate on that appHcations in which DHAP-dependent aldolase are part of a multi-enzyme system or, alternatively, on those in which the aldolase-catalyzed reaction is key in a multi-step synthetic pathway. 

The amino-acids that make up the primary structure of proteins will change their charge when the pH of the solution is altered due to their acid-base properties (Section 5.3 and Appendix 5.1). The effects of pH on enzyme-catalysed reactions can be complex since both Km and may be affected. Here, only the effects on Kmax are considered, as this usually reflects a single constant rather than several that may be associated within the constant Km (see Section 5.4.4.). It is assumed that pH does not change the limiting step in a multi-step process and that the substrate is saturating at all times. 

Utilization of whole cells and tissues in biosensor has increasingly been used. Enzyme stability, availability of different enzymes and reaction systems, and characteristics of cell surface are the advantages of using cells and tissues in biosensor designs. Multi-step enzyme reactions in cells also provide mechanisms to amplify the reactions that result in an increase in the detectability of the analytes. The presence of cofactors such as NAD, NADP, and metals in the cells allows the cofactor-dependent reactions to occur in the absence of reagents. (34, 50, 69). However, the diffusion of analytes through cell wall or membrane imposes constraint to this type of biosensors and results in a longer response time compared to the enzyme biosensors. 

We apply the concept of catalytic commitment, as proposed by Northrop, O Leary, and Cleland for multistep enzyme-catalyzed processes, to nonenzy-mic decarboxylation for comparison.52 The interpretation of CKIEs for decarboxylation reactions is dependent upon whether the process is viewed as a single-step or multi-step process. In a single-step mechanism, carbon-carbon bond-breaking is not affected by any other rate-limiting process. In this case, the CKIE for a particular compound will be constant under a standard set of conditions. Substantial changes in bond order must occur in the... 

The immobilization of enzymes on solid supports is the oldest of new biotechnologies. As for most of the chemical applications, the uses in this field require a multi-step modification. As a first layer a simple silane, mostly APTS, is used. In order to minimize sterical hindrance in the ultimate application reaction, a spacer molecule is often introduced between the active surface group and the immobilizing species. This may either be introduced at once, using a long-chain functional silane, or in a second step, after silanization. 

While the application of enzymes and proline as catalysts for the (commercial) formation of carbon-carbon bonds is relatively new, transition metal catalysts are well established for the industrial synthesis of carbon-carbon bonds. Although in themselves not always perfectly green, transition metal catalysts often allow the replacement of multi-step and stoichiometric reaction sequences with one single catalytic step. Thus, the overall amount of waste generated and energy used is reduced drastically [61-64]. 

Eigen and his colleagues went deep into biochemistry in the 1960s. They could measure enzyme mechanisms. They could measure the single steps in multi-step reactions and they called their method relaxation spectrometry. As a result of these studies they realized that the enz TOe reactions are optimal. They are fast, as fast as possible, but this is only one aspect. In fact, there are two counteracting principles to consider. One is that the enzyme has to be very specific for its substrate. This is a very specific catalysis and only this way can a complex reaction scheme be controlled. 

Catalytic aldol reactions are among the most useful synthetic methods for highly stereo-controlled asymmetric synthesis. In this account we discuss the recent development of a novel synthetic technique which uses tandem enzyme catalysis for the bi-directional chain elongation of simple dialdehydes and related multi-step procedures. The scope and the limitations of multiple one-pot enzymatic C-C bond formations is evaluated for the synthesis of unique and structurally complex carbohydrate-related compounds that may be regarded as metabolically stable mimetics of oligosaccharides and that are thus of interest because of their potential bioactivity. 

Achievements made wifhin fhe field of reaction engineering will increase fhe applicability of biocatalysts even more. For example, the use of microreactors is still in its infancy. Cascade catalysis and multi step conversions [81], a common domain of biocatalysis, will boost the application of biocatalysis for the transformation of highly reactive compounds or intermediates. Moreover, this might diminish operating time and costs as well as consumption of auxiliary chemicals and use of energy. For example, Bacher et al. published fhe six-step synthesis of labelled riboflavin using eight different enzymes in one reaction vessel [82]. 

Performing multiple reactions simultaneously in a single step offers possibilities for reduced waste and increased safety as well as manipulation of equilibria. This approach was inspired by the action of enzymes, which constitute interesting examples of multifunctional catalysts as they can promote multi-step reactions. In fact, enzymes immobilize mutually incompatible functional groups in a manner that maintains their independent functionality and, as such, are able to carry out multi-step reaction sequences with functionalities that would not be tolerated together in solution. 

The second problem arises from the multi-step nature of enzyme reactions by the time electronic demand has been altered sufficiently to see a trend, the rate-determining step may have been changed. 

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