The oxidation of phenolic compounds catalysed by cytochrome C peroxidase. Comparison with other peroxidases

The catalytic oxidations of a series of para-substituted phenolic compounds by cytochrome c peroxidase and hydrogen peroxide have been investigated. In the oxidation of these substrates the enzyme exhibits very low catalytic efficiency and little selectivity, compared to horseradish peroxidase and chloroperoxidase. The main reason for such a low activity seems the limited size of the access channel leading from the outside of the protein to the haem delta-meso edge, where the substrate binding and electron transfer to the haem apparently occur. Support to this view comes from preliminary relaxation rate measurements. These show that the phenolic substrates can actually approach the iron site but the nonlinearity of the relaxation rate vs. enzyme bound fraction plots is indicative of a process limited by chemical exchange.