The crystal structure of the GcoA enzyme and its mutants in complex with different ligands are used as the initial structures in this study (Table ). The protonation states of the side chains of the titratable amino acids were assessed using H++ server 30 at pH 7.5 that corroborating well with the previous literature. The force field parameters for the hemeiron in different states (resting and Cpd I) were taken from the previous literature. The forcefield parameters for syringol, guaiacol, and 3MC were developed using the general Amber force field (GAFF). The partial charges of these compounds were calculated with the RESP ( restrained electrostatic potential ) method of a QM optimized geometry using Gaussian 16 package at HF/6-31G* level of theory. The complex structure of GcoA in complex with (3-Methoxycatechol) 3MC was obtained by flexible docking of 3MC in WT and F169A mutant of CYP450GcoA enzyme using AutoDock4.2 (see SI for more details). We used Amber ff19SB force field for protein molecules, and the TIP3P water model for the solvents.