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PETN reductase as a versatile biocatalyst for the reduction of nitroalkenes
[Thesis]. Manchester, UK: The University of Manchester; 2012.
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Abstract
PETN reductase is a robust flavin-dependent oxidoreductase which demonstrates a broad substrate spectrum constituting industrially valuable C=C double bond reductions; specifically providing an efficient route to chiral nitroalkanes. The kinetic characterisation of PETN reductase with three commercially available nitro compounds establishes their viability as substrates for the enzyme, while also identifying preferable substrate structural characteristics. PETN reductase demonstrates activity with a novel range of β,β-disubstituted and α,β-disubstituted nitroalkenes. Methyl group positioning at the substrate β- or α-carbon is demonstrated to dictate the mechanism of reduction invoked by the enzyme, while the (Z)-isomers of such substrates are shown to be preferred (product ee’s up to >99 %). The crystal structure of the enzyme complex with 1-nitrocyclohexene reveals the presence of two binding conformations, only one of which is catalytically active. A site-directed mutagenesis study involving key active site residues identified a switch of stereopreference in the T26S PETN reductase mutant and determined that Tyr 186 is not essential for the reduction of nitroalkenes in PETN reductase.