The local electric field (LEF) of both enzymes, P450OleT and P450BSβ were calculated by means of the in-house program TITAN. To qualify the effect of the active site residues only, we stripped all protein and water molecules beyond 3Å of the Heme and substrate, such that both enzymes (the and Heme-Cys/substrate systems of P450OleT / P450BSβ) were subjected to the LEFs exerted respectively by H85/Q85, R245/R242, P246/P243, and two water molecules. Therefore, it is clear that the change in the LEF will be mainly due to the difference by H85 vs. Q85. The LEF was calculated along Fe-O axis, projecting on the O atoms of both enzymes. Similarly, the dipole moments (𝜇) for the QM/MM optimized bare heme-Cysteine/substrate systems were determined with Turbomole 7.31. The stabilization energies were calculated by use of equation 1: 41