Journal of Bioenergetics and Biomembranes

, Volume 26, Issue 6, pp 599–608

The histidine cycle: A new model for proton translocation in the respiratory heme-copper oxidases

  • Joel E. Morgan
  • Michael I. Verkhovsky
  • Mårten Wikström
Article

DOI: 10.1007/BF00831534

Cite this article as:
Morgan, J.E., Verkhovsky, M.I. & Wikström, M. J Bioenerg Biomembr (1994) 26: 599. doi:10.1007/BF00831534

Abstract

A model of redox-linked proton translocation is presented for the terminal heme-copper oxidases. The new model, which is distinct both in principle and in detail from previously suggested mechanisms, is introduced in a historical perspective and outlined first as a set of general principles, and then as a more detailed chemical mechanism, adapted to what is known about the chemistry of dioxygen reduction in this family of enzymes. The model postulates a direct mechanistic role in proton-pumping of the oxygenous ligand on the iron in the binuclear heme-copper site through an electrostatic nonbonding interaction between this ligand and the doubly protonated imidazolium group of a conserved histidine residue nearby. In the model this histidine residue cycles between imidazolium and imidazolate states translocating two protons per event, the imidazolate state stabilized by bonding to the copper in the site. The model also suggests a key role in proton translocation for those protons that are taken up in reduction of O2 to water, in that their uptake to the oxygenous ligand unlatches the electrostatically stabilized imidazolium residue and promotes proton release.

Key words

Proton-pumpingcytochrome oxidaseoxygen reduction

Copyright information

© Plenum Publishing Corporation 1994

Authors and Affiliations

  • Joel E. Morgan
    • 1
  • Michael I. Verkhovsky
    • 1
  • Mårten Wikström
    • 1
  1. 1.Helsinki Bioenergetics Group, Institute of Biomedical Sciences, Department of Medical ChemistryUniversity of HelsinkiFinland