Figure shows the two conformations of the distal tosyl azide (TAZ) of P411; before and after MD simulations. As can be seen from Figure , the TAZ is initially far from the heme iron (the respective distance between N1 and Fe is 4.6 Å). However, during the simulation, the distance reduces to 2.53Å (See Figure ) for 30% of the sampled MD trajectory. A closer inspection of the MD trajectory also shows that the proximity of the distal ligand with heme-iron is strongly correlated with the juxtapositions of L263 and V328 (See Figure for graphs showing the correlation with distance). It is apparent that these residues provide a tight packing to the distal ligand, and therefore, the relative position of these residues directly affects the orientation of the ligand. For the mechanism of formation of the active oxidant, iron nitrenoid, we followed with QM/MM calculations for a representative snapshot from MD simulations. We started the calculations with the optimization of the reactant followed by potential energy scanning to trace the reaction coordinate for the formation of the iron nitrenoid. The energy profile for the reaction is shown in Figure . As can be seen, the activation barrier for the formation of active oxidant i.e., iron nitrenoid, is just 2.6 kcal/mol. Moreover, this process takes place in a concerted displacement reaction; the Fe-N1 bond is formed and at the same time the N1-N2 bond is broken leaving behind the active oxidant iron nitrenoid and molecular nitrogen. As such, our QM/MM calculations show that the rate of formation of the iron nitrenoid active oxidant is by far faster than that of the analogous process which generates Cpd I for the native CYP450BM3 enzyme where cysteine is the axial ligand. The corresponding barrier for this Cpd I formation process is 15.7 kcal/mol. Hence, our theoretical mechanistic investigation shows that the engineered enzyme produces the iron nitrenoid more efficiently than its functional analog Cpd I in the native P450 enzyme.