title: Adaptation of aerobic respiration to low O2 environments.
abstract: Aerobic respiration in bacteria, Archaea, and mitochondria is performed by oxygen reductase members of the heme-copper oxidoreductase superfamily. These enzymes are redox-driven proton pumps which conserve part of the free energy released from oxygen reduction to generate a proton motive force. The oxygen reductases can be divided into three main families based on evolutionary and structural analyses (A-, B- and C-families), with the B- and C-families evolving after the A-family. The A-family utilizes two proton input channels to transfer protons for pumping and chemistry, whereas the B- and C-families require only one. Generally, the B- and C-families also have higher apparent oxygen affinities than the A-family. Here we use whole cell proton pumping measurements to demonstrate differential proton pumping efficiencies between representatives of the A-, B-, and C-oxygen reductase families. The A-family has a coupling stoichiometry of 1 H(+)/e(-), whereas the B- and C-families have coupling stoichiometries of 0.5 H(+)/e(-). The differential proton pumping stoichiometries, along with differences in the structures of the proton-conducting channels, place critical constraints on models of the mechanism of proton pumping. Most significantly, it is proposed that the adaptation of aerobic respiration to low oxygen environments resulted in a concomitant reduction in energy conservation efficiency, with important physiological and ecological consequences.
authors.affiliation: Center for Biophysics and Computational Biology, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Huazhi
authors.initials: H
authors.lastname: Han
authors.forename: James
authors.initials: J
authors.lastname: Hemp
authors.forename: Laura A
authors.initials: LA
authors.lastname: Pace
authors.forename: Hanlin
authors.initials: H
authors.lastname: Ouyang
authors.forename: Krithika
authors.initials: K
authors.lastname: Ganesan
authors.forename: Jung Hyeob
authors.initials: JH
authors.lastname: Roh
authors.forename: Fevzi
authors.initials: F
authors.lastname: Daldal
authors.forename: Steven R
authors.initials: SR
authors.lastname: Blanke
authors.forename: Robert B
authors.initials: RB
authors.lastname: Gennis
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D000332:Aerobiosis / Q000187:drug effects; D001419:Bacteria / Q000187:drug effects* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D010100:Oxygen / Q000494:pharmacology; D017494:Proton Pumps / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000187:drug effects / Q000378:metabolism
chemical_list: D017494:Proton Pumps; D010100:Oxygen