Chemistry With Monooxygenases

The regio- and stereoselective hydroxylation of specific nonactivated carbon atoms is a very useful reaction. For example, it can be used for the functionalization of alkanes and for the preparation of chiral alcohols that are useful pharmaceutical intermediates. This type of transformation is, however, a significant challenge in classic chemistry. On the other hand, Nature has found a general solution to this challenge via the development of a large number of monooxygenases, some of which, such as the soluble cytochrome P450 monooxygenases (P450 cam, P450 BM-3), soluble methane monooxygenase (sMMO), and membrane-bound alkane hydroxylase (AlkB) of Pseudomonas putida GPo1, have been well investigated. Their synthetic applications are limited, however, due to narrow substrate ranges or poor selectivity. The filamentous fungus Beauveria bassiana ATCC 7159 is often used for laboratorial synthesis,21 because it contains one or more unknown oxygenase systems, but these generally show low activities and selectivities. Thus, for specific hydroxylations, it is generally necessary to find appropriate biocatalysts.

To search for an appropriate whole-cell biocatalyst, it is necessary to identify an organism that contains large amounts of the desired enzyme. Equally important, the organism should not contain related pathway enzymes that modify or destroy the product synthesized by the desired enzyme.

In addition, the substrate and product should be transported through the cell membrane, either passively or actively, and necessary cofactors should be regenerated. Finally, the specific organism used should function well in an optimized bioreactor system.22,23 All of these requirements can be met by using strains that contain the desired enzyme in question.

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