Direct electron transfer between graphite electrodes and ligninolytic peroxidases from Phanerochaete chrysosporium

Electron transfer (ET) of ligninolytic peroxidases was studied in the bioelectrocatalytic reduction reaction of H2O2 at peroxidase-modified graphite electrodes. Specifically, native lignin (LiP) and manganese (MnP) peroxidases secreted by Phanerochaete chrysosporium, as well as a few different recombinant MnP forms were used in the electrochemical studies. The recombinant enzymes included wild-type MnP and three mutants with genetically engineered ligninolytic activity. Rotating disk electrode experiments performed at 0 V (vs. SCE) in 0.1 M potassium phosphate buffer (PBS), pH 7.0, demonstrated that LiP and the various forms of MnPs display a significant bioelectrocatalytic activity for the reduction of H2O2 being very similar to that known for HRP. The heterogeneous ET rate constants, calculated from the data on direct and mediated ET, ranged between 1 and 2 s(-1) implying a similarity of the ET pathways, graphite surface-active site of the peroxidases. For H2O2 concentrations below 20 muM the sensitivity of the MnP-modified electrodes for H2O2 was slightly higher than that of horseradish peroxidase (HRP)-modified electrodes, correlating well with a higher rate of formation of compound E1. The very similar heterogeneous ET data for HRP and the ligninolytic peroxidases did not at all reflect the difference in their homogeneous activity towards ABTS being 1400 U mg(-1) for HRP and ranging between 0.02 and 8 U mg(-1) for the ligninolytic peroxidases. The recombinant nonglycosylated form of MnP with enhanced veratryl alcohol oxidizing activity (MnP mutant S168W) was shown to possess the most promising bioelectrocatalytic properties for a possible further development of a MnP-based biosensor/biocatalyst for the detection/depolymerization of lignin.