Enzymatic and physiological properties of the tungsten-substituted molybdenum TMAO reductase from Escherichia coli

The trimethylamine N-oxide (TMAO) reductase of Escherichia coli is a molybd oenzyme that catalyses the reduction of the TMAO to trimethylamine (TMA) wi th a redox potential of + 130 mV. We have successfully substituted the moly bdenum with tungsten and obtained an active tungsto-TMAO reductase. Kinetic studies revealed that the catalytic efficiency of the tungsto-substituted TMAO reductase (W-TorA) was increased significantly (twofold), although a d ecrease of about 50% in its k(cat) was found compared with the molybdo-TMAO reductase (Mo-TorA). W-TorA is more sensitive to high pH, is less sensitiv e to high NaCl concentration and is more heat resistant than Mo-TorA. Most importantly, the W-TorA becomes capable of reducing sulphoxides and support s the anaerobic growth of a bacterial host on these substrates. The evoluti onary implication and mechanistic significance of the tungsten substitution are discussed.