The cytochrome ba3 oxygen reductase from Thermus thermophilus uses a single input channel for proton delivery to the active site and for proton pumping

Hsin Yang Chang, James Hemp, Ying Chen, James A. Fee, Robert B. Gennis

Research output: Contribution to journalArticlepeer-review


The heme-copper oxygen reductases are redox-driven proton pumps that generate a proton motive force in both prokaryotes and mitochondria. These enzymes have been divided into 3 evolutionarily related groups: the A-, B- and C-families. Most experimental work on proton-pumping mechanisms has been performed with members of the A-family. These enzymes require 2 proton input pathways (D- and K-channels) to transfer protons used for oxygen reduction chemistry and for proton pumping, with the D-channel transporting all pumped protons. In this work we use site-directed mutagenesis to demonstrate that the ba3 oxygen reductase from Thermus thermophilus, a representative of the B-family, does not contain a D-channel. Rather, it utilizes only 1 proton input channel, analogous to that of the A-family K-channel, and it delivers protons to the active site for both O2 chemistry and proton pumping. Comparison of available subunit I sequences reveals that the only structural elements conserved within the oxygen reductase families that could perform these functions are active-site components, namely the covalently linked histidine-tyrosine, the CuB and its ligands, and the active-site heme and its ligands. Therefore, our data suggest that all oxygen reductases perform the same chemical reactions for oxygen reduction and comprise the essential elements of the proton-pumping mechanism (e.g., the proton-loading and kinetic-gating sites). These sites, however, cannot be located within the D-channel. These results along with structural considerations point to the A-propionate region of the active-site heme and surrounding water molecules as the proton-loading site.

Original languageEnglish (US)
Pages (from-to)16169-16173
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number38
StatePublished - Sep 22 2009


  • Cytochrome c oxidase
  • Respiratory enzymes

ASJC Scopus subject areas

  • General

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