Biocatalyst structure

Matsunaga I, Shiro Y (2004) Peroxide-utilizing biocatalysts structural and functional diversity of heme-containing enzymes. Curr Opin Chem Biol 8 127-132... 

Upon mutagenesis of the monoamine oxidase from Aspergillus niger (MAO-N) within several rounds of directed evolution [65], variant biocatalysts were identified with largely expanded substrate acceptance, enabling also the deracemization of tertiary amines incorporating straight-chain and cyclic structural motifs [66]. 

Membrane-integrated proteins were always hard to express in cell-based systems in sufficient quantity for structural analysis. In cell-free systems, they can be produced on a milligrams per milliliter scale, which, combined with labeling with stable isotopes, is also very amenable forNMR spectroscopy [157-161]. Possible applications of in vitro expression systems also include incorporation of selenomethionine (Se-Met) into proteins for multiwavelength anomalous diffraction phasing of protein crystal structures [162], Se-Met-containing proteins are usually toxic for cellular systems [163]. Consequently, rational design of more efficient biocatalysts is facilitated by quick access to structural information about the enzyme. 

Rhodococcus sp. AJ270 was applied to the transformation of a number of racemic cis- and traray-3-aryl-2-methyloxiranecarbonitriles (Figure 8.7). In all cases, the NHase activity proceeded very rapidly and with poor enantioselectivity. In contrast, the amidase activity was strongly dependent upon substrate structure. In general, the biocatalyst displays a strong preference for the unsubstituted phenyl side chain or /wa-substituted phenyl side chain compared with ortho- or meta-, and this is manifest both with respect to observed conversion and rate and also observed enantioselectivity. In contrast, the biotransformations of... 

As referred to previously, if the active site of a biocatalyst is close enough to the electrode surface, direct electron transfer to/from an electrode can result. It has been shown in recent years that direct electron transfer from the GOx active site is possible using appropriate electrode preparation procedures. These preparation procedures usually aim to provide nano-structured features on the electrode surface that can penetrate sufficiently the GOx active site to allow for direct electron transfer. The direct electron... 

However, while it is clear that biocatalysts may only provide viable and reliable methods in about 5-10% of all transformations of interest to synthetic organic chemists, it is also clear that in some cases the biotransformation will provide the key step in the best method in going from a cheap substrate to a high value, optically active fine chemical. Thus ignoring biotransformations altogether means one may occasionally overlook the best pathway to a target structure. 

Because the monoliths allow total convection of the mobile phase through their pores, the overall mass transfer is dramatically accelerated compared to conventional porous structures. Based on the morphology and porous properties of the molded monoliths, which allow fast flow of substrate solutions, it can be safely anticipated that they would also provide outstanding supports for immobilization of biocatalysts, thus extending the original concept of monolithic materials to the area of catalysis. 

Investigations of enzyme-catalyzed direct electron transfer introduce the basis for a future generation of electrocatalysts based on enzyme mimics. This avenue could offer new methods of synthesis for nonprecious metal electrocatalysts, based on nano-structured (for example, sol—gel-derived) molecular imprints from a biological catalyst (enzyme) with pronounced and, in some cases, unique electrocatalytic properties. Computational approaches to the study of transition state stabilization by biocatalysts has led to the concept of theozymes . " ... 

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