Multifrequency electron
paramagnetic
resonance (EPR) spectra of the Cu(II) site in bovine heart cytochrome c
oxidase (COX) and nitrous oxide reductase (N2OR)
from
Pseudomonas stutzeri confirm the existence of Cu-Cu interaction
in both enzymes. C-band (4.5 GHz) proves to be a particularly good
frequency
complementing the spectra of COX and N2OR
recorded
at 2.4 and 3.5 GHz. Both the high and low field region of the EPR
spectra
show the presence of a well-resolved 7-line pattern consistent with the
idea of a binuclear Cu center in COX and N2OR.
Based
on this assumption consistent g-values are calculated for
gz
and gx at four frequencies. No
consistent g-values
are obtained with the assumption of a 4-line pattern indicative for a
mononuclear
Cu site.