E. coli Nickel‐Iron Hydrogenase 1 Catalyses Non‐native Reduction of Flavins: Demonstration for Alkene Hydrogenation by Old Yellow Enzyme Ene‐reductases**

Abstract

A new activity for the [NiFe] uptake hydrogenase 1 of Escherichia coli (Hyd1) is presented. Direct reduction of biological flavin cofactors FMN and FAD is achieved using H 2 as a simple, completely atom-economical reductant. The robust nature of Hyd1 is exploited for flavin reduction across a broad range of temperatures (25-70 8C) and extended reaction times. The utility of this system as a simple, easy to implement FMNH 2 or FADH 2 regenerating system is then demonstrated by supplying reduced flavin to Old Yellow Enzyme "enereductases" to support asymmetric alkene reductions with up to 100 % conversion. Hyd1 turnover frequencies up to 20.4 min À1 and total turnover numbers up to 20 200 were recorded during flavin recycling. Scheme 1. Oxidized (left) and reduced (right) FMN or FAD cofactors.