KatG from HALOARCULA MARISMORTUI (Hm), used concomitantly with initiator (H2O2), exhibits high catalase and peroxidase activities with substrate (ODA). The distal side M244–Y218–W95 covalent adduct and M244 centered octahedral coordination complexes in the active site are essential for the catalase activity. Mass spectroscopic analysis of the M244A shows cleavage of the covalent adduct between Y214–W95 and M244 without its sulfer atom. Crystal structure of M244A variant in HmKatG has the geometrically dimeric subunits that disrupted or not a π–interaction which is linked between heme edge (C1C) to the adduct end W95 (Nε1). The isoenzyme pattern of peroxidase was determined by fitting the kinetic data to non-linear (mixed) Michaelis-Menten equation and then governed by the hetero-dimeric characters. Respective peroxidase catalytic efficiency for two subunits was 2.5 and 4.8 -fold increased with higher binding affinity for ODA. It was enhanced by rotating the dihedral angle χ2 of D125.