Modification of heme c binding motifs in the small subunit (NrfH) of the Wolinella succinogenes cytochrome c nitrite reductase complex

The two multiheme c-type cytochromes NrfH and NrfA form a membrane-bound complex that catalyzes menaquinol oxidation by nitrite during respiratory nitrite ammonification of Wolinella succinogenes. Each cysteine residue of the four NrfH heme c binding motifs was individually replaced by serine. Of the resulting eight W. succinogenes mutants, only one is able to grow by nitrite respiration although its electron transport activity from formate to nitrite is decreased. NrfH from this mutant was shown by matrix-assisted laser desorption/ionization mass spectrometry to carry four covalently bound heme groups like wild-type NrfH indicating that the cytochrome c biogenesis system 11 organism W. succinogenes is able to attach heme to an SXXCH motif. (C) 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.