Microperoxidases are used as model compounds for hemoproteins and have potential applications as labels for antibodies, as electron transfer mediators, in biosensors and biofuel cells. Their relative structural simplicity yet possessing peroxidase activity, and the presence of chemical functions suited for covalent coupling or modification are the advantages for practical applications in the biological and medical research fields.

Direct electron transfer (DET) between an immobilized redox enzyme and an electrode is one of the central themes in bioelectrochemistry, being one of the most interesting transduction processes for the development of fast responding amperometric biosensors. In order to obtain a high-speed, efficient DET one has to take into consideration the importance of interfacial interactions, the structure of biolayers and the distance between the active site of the biomolecule and the electrode.

As a continuation of our previous work on the electrochemistry of microperoxidase-11 immobilized onto gold electrodes in different ways, we here report on the electrochemistry of an artificial his-tagged microperoxidase (MP-86), obtained in vivo, using the cytochrome c secretion and maturation machinery of E. coli. The artificial heme-containing oligopeptide possesses a classical heme c binding signature sequence followed by a 6xhis-tag. The his-tag facilitates purification and stabilizes the heme group but also enables specific immobilization of the polypeptide onto solid surfaces.

Cyclic voltammetry and flow injection amperometry are the basic electrochemical techniques used in this study. The immobilized microperoxidase assembled as a monolayer onto gold undergoes a rapid, reversible electron transfer. The 6xhis-tag favors both adsorption onto naked gold electrodes and specific immobilization using Ni-NTA technology, conserving a short distance between the heme group and the electrode. In order to demonstrate the peroxidase activity of MP-86, electrocatalytic reduction of hydrogen peroxide in a flow system was also performed.

Acknowledgement. This work was supported by the European Commission (MEST-CT-2004-514743) and The Swedish Research Council.

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