The substrate oxygenation kinetics were determined from NO - 2 formation of selected enzymesubstrate combinations. Experiments were performed in triplicate in 1.5 mL plastic tubes containing 0.5 mL MES buffer (50 mM, pH 6. To determine maximum rates (ν i max ) and Michaelis constants (K i m ) of NO - 2 formation in the presence of different substrates, i, we performed a non-linear least square regression according to equation S2,