Enzymatic activity of the alternative complex III as a menaquinol:auracyanin oxidoreductase in the electron transfer chain of Chloroflexus aurantiacus

FEBS Lett. 2009 Oct 6;583(19):3275-9. doi: 10.1016/j.febslet.2009.09.022. Epub 2009 Sep 13.


The surprising lack of the cytochrome bc1 complex in the filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus suggests that a functional replacement exists to link the cyclic electron transfer chain. Earlier work identified the alternative complex III (ACIII) as a substitute of cytochrome bc1 complex. Herein, the enzymatic activity of ACIII is studied. The results strongly support the view that the ACIII functions as menaquinol:auracyanin oxidoreductase in the C. aurantiacus electron transfer chain. Among all the substrates tested, auracyanin is the most efficient electron acceptor of ACIII, suggesting that ACIII directly transfers the electron to auracyanin instead of cytochrome c-554. The lack of sensitivity to common inhibitors of the cytochrome bc1 complex indicates a different catalytic mechanism for the ACIII complex.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / metabolism*
  • Chloroflexus / enzymology*
  • Electron Transport
  • Electron Transport Complex III / metabolism*
  • Metalloproteins / metabolism*
  • Quinone Reductases / metabolism*
  • Vitamin K 2 / analogs & derivatives*
  • Vitamin K 2 / metabolism


  • Bacterial Proteins
  • Metalloproteins
  • auracyanin A protein, bacteria
  • Vitamin K 2
  • menatetrenone
  • Quinone Reductases
  • Electron Transport Complex III