Biocatalytic Versions

The first indication of the existence of so-called Baeyer-Villiger monooxygenases (BVMOs) was reported in the late 1940s [56]. It was observed that certain fungi were able to oxidize steroids via a BV reaction [56], but two decades elapsed before the first BVMOs were isolated and characterized [57, 58]. All characterized BVMOs contain a flavin cofactor that is vital for the catalytic activity of the enzyme, Furthermore, NADH or NADPH cofactors are needed as electron donors. Careful inspection of all available biochemical data on BVMOs has revealed that at least two discrete classes of BVMOs exist, types I and II [59]. 

Type I and Type II BVMOs Type I BVMOs consist of only one polypeptide of about 500 amino acids with the cofactor flavin adenine dinucleotide (FAD) tightly bound into the structure, and is dependent on NADPH for activity [60]. Most offlie presently known BVMOs are of this type, and are typically soluble proteins located in the cytosol of bacteria or fungi, which is in contrast to many other monooxygenase systems that often are found to be membrane bound or membrane associated. They contain two Rossmann sequence motifs, GxGxxG, which indicate that these enzymes bind the two cofactors (FAD or NADPH) using separate dinucleotide binding domains [61]. 

Other BVMOs Recent findings of several enzymes that display Baeyer-Villiger activity, although they do not resemble the above-mentioned BVMOs, suggest that at least two other BVMO classes exist ]63]. 

A flavoprotein monooxygenase (MtmOIV) involved in the biosynthesis of mithra-mycin, and a heme-containing BVMO belonging to the cytochrome P450 superfamily have recently been reported ]64]. Both enzymes were shown to catalyze BV oxidations [65]. In addition, a plant enzyme turned out to be capable of modifying steroids via BV oxidation [66]. Further studies will reveal more mechanistic details concerning these newly identified BVMOs that may be useful for the development of new biocatalytic applications in the future. 

Cyclohexanone Monooxgenase (CH MOAdneto) Most biochemical and biocataiytic studies have been performed on Type I BVMOs [67], since they represent relatively uncomplicated monooxygenase systems, and several expression systems have been developed for a number of Type I BVMOs. 

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Fig. 2.20 Formal fitness landscape of various biocatalytic and inactive (i.e., the latter being located outside the window of essentiality ) metal ions for the carboxypeptidase A (Vallee and Williams 1968). The enzyme reconstituted by cobalt (treatment with EDTA, then addition of Co +) is considerably more active than the native Zn version , while Cd (and other ions) afford poorly to non-active metalloproteins in this case. (Relative) catalytic turnover rates are from Vallee and Williams 1968, x and c values this work and previous publications by this author. Here, sufficient abundance of the corresponding ions is taken for granted owing to in-vitro addition to apoprotein, so c k is not hmited by c, but merely represents the catalytic features pertinent to k, obtained from either biochemistry (several metal ions being present, e.g. in phosphatases) or experiments with reconstituted apoproteins...

Simeo, Y., Kroutil, W., Faber, K. Biocatalytic deracemization dynamic resolution, stereoin-version, enantioconvergent processes and cyclic deracemization. In Biocatalysis in the Pharmaceutical and Biotechnology Industries (ed. Patel, R.N.), 2007, CRC Press, Boca Raton, FL, 27-51. 

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