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Journal of Bacteriology, June 2005, p. 4077-4085, Vol. 187, No. 12
0021-9193/05/$08.00+0     doi:10.1128/JB.187.12.4077-4085.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Regulation and Function of Cytochrome c' in Rhodobacter sphaeroides 2.4.3

Peter S. Choi,^1, Vladimir M. Grigoryants,³ Hector D. Abruña,² Charles P. Scholes,³ and James P. Shapleigh^1*

Department of Microbiology, Wing Hall, Cornell University, Ithaca, New York 14853,¹ Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853,² Department of Chemistry, Center for Biophysics and Biochemistry, University at Albany, State University of New York at Albany, Albany, New York 12222³

Received 19 November 2004/ Accepted 9 March 2005

Cytochrome c' (Cyt c') is a c-type cytochrome with a pentacoordinate heme iron. The gene encoding this protein in Rhodobacter sphaeroides 2.4.3, designated cycP, was isolated and sequenced. Northern blot analysis and ß-galactosidase assays demonstrated that cycP transcription increased as oxygen levels decreased and was not repressed under denitrifying conditions as observed in another Rhodobacter species. CO difference spectra performed with extracts of cells grown under different conditions revealed that Cyt c' levels were highest during photosynthetic denitrifying growth conditions. The increase in Cyt c' under this condition was higher than would be predicted from transcriptional studies. Electron paramagnetic resonance analysis of whole cells demonstrated that Cyt c' binds NO during denitrification. Mass spectrometric analysis of nitrogen oxides produced by cells and purified protein did not indicate that Cyt c' has NO reductase activity. Taken together, these results suggest a model where Cyt c' in R. sphaeroides 2.4.3 may shuttle NO to the membrane, where it can be reduced.

Present address: NIDDK, Genetics and Biochemistry Branch, National Institutes of Health, Bethesda, MD 20892-0538.

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