Azo (NN) bond reduction by ene reductases.

Herein, we describe the discovery of a new catalytic promiscuity of ene reductases (EREDs), which enables the selective reduction of azoarenes to the corresponding hydroazoarenes using MorB. The role of active site residues is confirmed by generating H186A and N189A variants of MorB, which show considerable loss of activity towards azo bond reduction. This transformation expands the known catalytic repertoire of EREDs and provides a sustainable biocatalytic route to valuable hydroazo compounds.