Effect of modification of heme propionate groups on the reactivity of horseradish peroxidase

Artificial horseradish peroxidases were prepared containing hemin in which propionate groups at the 6,7-positions were modified. All of the unnatural molecules had the chemical and enzymic properties of the native enzymes but not to the same extent. This finding eliminates the possibility that a propionate group in the 6- or 7-position of the hemin plays a catalytic role in compound I formation. The main effect of modifications at the positions of heme carboxyl groups may be caused by changes in the electric charge at the periphery of the hemin.