The Protonation State of the Cross-linked Tyrosine during the Catalytic Cycle of Cytochrome c Oxidase

Cytochrome c oxidase is the terminal complex of the respiratory chain in mitochondria and some aerobic bacteria and is responsible for most of the O-2 consumption in biology. The key reaction in the catalysis of O-2 reduction is O-O bond scission that requires four electrons and a proton. In our recent work (Gorbikova, E. A., Belevich, I., Wikstrom, M., and Verkhovsky, M. I. ( 2008) Proc. Natl. Acad. Sci. U. S. A. 105, 10733-10737), it was shown that the cross-linked Tyr-280 ( Paracoccus denitrificans numbering) provides the proton for O-O bond cleavage. The deprotonated Tyr-280 must be reprotonated later on in the catalytic cycle to serve as a proton donor for the next oxygen reduction event. To find the reaction step at which the crosslinked Tyr-280 becomes reprotonated, all further steps of the catalytic cycle after O-O bond cleavage were followed by infrared spectroscopy. We found that complete reprotonation of the tyrosine is linked to the formation of the one-electron reduced state coupled to reduction of the Cu-B site.