Influence of tryptophan mutation on the direct electron transfer of immobilized tobacco peroxidase
A major challenge in the design of electrochemical biodevices is to achieve fast rates of electron exchange between proteins and electrodes. In this work, we show that a significant increase in the direct electron transfer rate between a graphite electrode and Tobacco Peroxidase takes place when a surface exposed leucine, located in the vicinity of the heme pocket, is replaced by tryptophan. The analysis of the Fe(III)/Fe(II) voltammetric responses of native and mutated proteins, as a function of solution pH and temperature, leads to similar values of the reduction entropy and reorganization energy, but to a higher electronic coupling in the case of the mutant. In addition, the mutated and native proteins are shown to display similar electrocatalytic activities to reduce hydrogen peroxide at positive potentials, indicating that the molecular structure of the heme pocket is largely unaffected by the mutation.