The role of the conserved tryptophan272 of the Paracoccus denitrificans cytochrome c oxidase in proton pumping

The catalytic mechanism of heme-copper oxidases - electron transfer coupled to proton pumping - is not yet fully understood. Single turnover experiments in which fully reduced cytochrome aa(3) from Paracoccus denitrificans reacts with O-2 using the microsecond freeze-hyperquenching sampling technique enabled trapping of transient catalytic intermediates and analysis by low temperature W-Visible, X-band and Q-band EPR spectroscopy. Our recent findings (Wiertz et al. (2007) J. Biol. Chem. 282, 31580-31591), which show that the strictly conserved W272 is a redox active residue are reviewed here. The W272 forms a tryptophan neutral radical in the transition F -> F-W* -> O-H in which the novel intermediate F-W* harbors the tryptophan radical. The potential role of W272 in proton pumping is highlighted. (C) 2008 Elsevier BY. All rights reserved.