Probing heme propionate involvement in transmembrane proton transfer coupled to electron transfer in dihemic quinol:fumarate reductase by 13C-labeling and FTIR difference spectroscopy

  • Mileni M
  • Haas A
  • Mäntele W
 et al. 
  • 10


    Mendeley users who have this article in their library.
  • 13


    Citations of this article.


Quinol:fumarate reductase (QFR) is the terminal enzyme of anaerobic fumarate respiration. This membrane protein complex couples the oxidation of menaquinol to menaquinone to the reduction of fumarate to succinate. Although the diheme-containing QFR from Wolinella succinogenes is known to catalyze an electroneutral process, its three-dimensional structure at 2.2 A resolution and the structural and functional characterization of variant enzymes revealed locations of the active sites that indicated electrogenic catalysis. A solution to this apparent controversy was proposed with the so-called "E-pathway hypothesis". According to this, transmembrane electron transfer via the heme groups is strictly coupled to a parallel, compensatory transfer of protons via a transiently established pathway, which is inactive in the oxidized state of the enzyme. Proposed constituents of the E-pathway are the side chain of Glu C180 and the ring C propionate of the distal heme. Previous experimental evidence strongly supports such a role of the former constituent. Here, we investigate a possible heme-propionate involvement in redox-coupled proton transfer by a combination of specific (13)C-heme propionate labeling and Fourier transform infrared (FTIR) difference spectroscopy. The labeling was achieved by creating a W. succinogenes mutant that was auxotrophic for the heme-precursor 5-aminolevulinate and by providing [1-(13)C]-5-aminolevulinate to the medium. FTIR difference spectroscopy revealed a variation on characteristic heme propionate vibrations in the mid-infrared range upon redox changes of the distal heme. These results support a functional role of the distal heme ring C propionate in the context of the proposed E-pathway hypothesis of coupled transmembrane electron and proton transfer.

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document


  • Mauro Mileni

  • Alexander H. Haas

  • Werner Mäntele

  • Jörg Simon

  • C. Roy D Lancaster

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free