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Figure 3.
Fig. 3. Proposed mechanism for substrate oxidation in
plant peroxidases. First, the active site arginine (Arg38 in
HRPC) donates a hydrogen bond to the phenolic oxygen of the
reducing substrate. This hydrogen bond will assist proton
transfer from the phenolic oxygen to active site histidine (His
42 in HRPC) through an active site water molecule held in
position by the backbone oxygen of a conserved proline residue
(Pro139 in HRPC). The electron is transferred to the heme group
via the C-18 methyl-C-20 heme edge. Then compound II reduction
is assisted by similar a proton transfer. The proton can be
transferred to the ferryl oxygen through the active site water
molecule situated equidistant between the distal histidine and
the expected position of the ferryl oxygen of compound II,
regenerating the resting state enzyme and a water molecule.
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