While there is broad agreement on the catalytic mechanism of Multicopper Oxidases (MCOs), the geometric and electronic structures of the resting trinuclear Cu cluster have been variable, and their relevance to catalysis debated. Here, we present a spectroscopic characterization, complimented by crystallographic data, of two resting forms occurring in the same enzyme, and define their interconversion. The resting oxidized form shows similar features to the resting form in Rhus vernicifera and Trametes versicolor laccase, characterized by ‘normal’ type 2 Cu EPR features, 330nm absorption shoulder, and a short type 3 (T3) Cu-Cu distance, while the alternative resting form shows unusually small A-parallel and high g-parallel EPR features, lack of 330nm absorption intensity, and a long T3 Cu-Cu distance. These different forms are evaluated with respect to activation for catalysis, and it is shown that the alternative resting form can only be activated by low-potential reduction, in contrast to the resting oxidized form which is activated via the type 1 Cu at high potential. This difference in activity is correlated to differences in redox states of the two forms, and highlights the requirement for efficient sequential reduction of resting MCOs for their involvement in catalysis.
3 pagesInternational audienceA new generation of mediatorless H2/O2 biofuel cells was designed based on a hyperthermophilic O2-tolerant hydrogenase and a thermostable bilirubin oxidase both immobilized on carbon nanofibers. A power density up to 1.5±0.2 mW*cm−2 at 60 °Cwas reached. This first demonstration of a H2/O2 biofuel cell able to deliver electricity over awide range of temperatures, from30 °C up to 80 °C, and over a large pHwindow, allows considering this device as an alternative power supply for small portable applications in various environments, including extreme ones
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