The simulation of variant 1 reveals two conformations; (a) initial and less populated (~20%) conformations which we refer to as the minor basin, and is shown by green coloring in Figure ; and (b) the highly populated conformations (80%) which is the major basin, shown by orange in Figure . In the minor basin, the substrate is close to the iron nitrenoid (~3.5 Å), and at the same time, an active site residue F263 is located perpendicular to the substrate. The perpendicular orientation of F263 (green in Figure ) applies a restraint on the substrate and limits its flexibility. On the other hand, as shown by the orange color in Figure , in the major basin the substrate moves away from the active oxidant (7-10 Å), and subsequently, the F263 residue flips to a parallel position vis-à-vis the substrate. This reorientation of the F263 frees the substrate from any restraint and, in turn, the substrate acquires flexibility. This might be the root cause for the low activity and less specificity of the substrate in variant 1. It is apparent, therefore, that the MD simulation concisely explains the low activity and specificity for variant 1. In summary, the Phenylalanine residue (F263) acts as a ringmaster which controls the substrate movement inside the active site by changing its conformation from perpendicular to parallel orientation. As stated earlier, the mutations of A82L, A78V, and F263L in variant 2 significantly enhance the C-H amination activity and enantioselectivity (>99%) relative to variant 1. Therefore, we performed MD simulations for this variant to uncover the roots for this change in activity.