Amino Acid Sequence of Pwczcoccus denitrificans Cytochrome chsO*

The amino acid sequence of Paracoccus (formerly Micrococcus) denitrificans cytochrome chbO has been established by a combination of standard chemical techniques and interpretation of a 2.5 8, resolution x-ray electron density map. Peptides derived from a trypsin digest were chemically sequenced, and then ordered by fitting them to the density map. The amino acid compositions of chymotryptic peptides confirmed the x-ray map ordering the tryptic peptides. The amino acid sequence of this respiratory, prokaryotic cytochrome with 134 residues is discussed in relation to those of eukaryotic respiratory cytochrome c (103 to 113 amino acids), and prokaryotic, photosynthetic cZ (103 to 124 amino acids). At the primary structure level, c and cbbO differ no more from cytochromes c2 than the various cytochromes cZ do from one another. It is suggested that the respiratory electron transport chain in prokaryotes and eukaryotes is a relatively late evolutionary offshoot of the photosynthetic electron transport chain in purple non-sulfur bacteria.