[Todos] Seminario INQUIMAE/DQIAyQF Martes 9 de diciembre, 13 hs

[Andrea Peralta]

Martes 9-12-2014, 13 hs. Aula Seminarios, INQUIMAE, 3er piso

INSIGHTS INTO THE MOLECULAR MECHANISMS OF HETEROGENEOUS DIRECT AND
MEDIATED ELECTRON TRANSFER BETWEEN BILIRUBIN OXIDASE FROM MYROTHECIUM
VERRUCARIA AND GRAPHITE ELECTRODES

Federico Tascaa, Diego Fariasa, Carmen Castroa, Peter Ó. Conghaileb,
Donald Leechb

a Departamento de Ciencias de los Materiales, Facultad de Química y
Biología, Universidad de Santiago de Chile, Santiago, Chile.
bDepartment of Chemistry, National University of Ireland, Galway, Ireland.

Federico.tasca en usach.cl

Multicopper Oxidases (MCOs) utilize a minimum of four Cu ions, and various
reducing substrates, to reduce O2 to H2O. High substrate potentials,
combined with a low overpotential for dioxygen reduction, have made these
enzymes attractive for industrial and bioelectrochemical applications.
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
has been debated. Here, we present an electrochemical characterization, of
two resting forms occurring in the same enzyme and define their
interconversion. 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 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.
Direct electro-catalytic reduction (Direct Electron Transfer, DET) of
oxygen to water was obtained on spectrographite electrodes modified by
physical adsorption of bilirubin oxidases from Myrothecium verrucaria
BOD1. Moreover the enzyme was cross-liked to a high potential Os redox
polymer which actuated as a mediator for the mediated electron transfer
(MET) from the trinuclear Cu cluster to the electrode. The existence of an
alternative resting form of the enzyme 2,3 and the effect of temperature,
pH, and chloride on the catalytic cycle are analyzed in the presence and
in the absence of the OS redox polymer.

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