Nitrobacter agilis Cytochrome c-550: Isolation, Physicochemical and Enzymatic Properties, and Primary Structure

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Abstract
Nitrobacter agilis cytochrome c-550 was purified to an electrophoretically homogeneous state, and some of its properties were determined. The cytochrome showed an absorption peak at 410 nm in the oxidized form, and peaks at 416, 521 and 550 nm in the reduced form. Its isoelectric point was 8.1 at 5°C. Analysis of the amino acid composition showed that the cytochrome molecule was composed of 108 amino acid residues, 16 of which were lysine residues. The cytochrome reacted rapidly with N. agilis cytochrome c oxidase and yeast cytochrome c peroxidase and more slowly with Pseudomonas aeruginosa nitrite reductase and bovine cytochrome c oxidase. The reactivities with these redox enzymes suggested that the cytochrome might be an evolutionary stage between bacterial and eukaryotic cytochromes c. The primary structure of the cytochrome from the N-terminus to the 85th residue was determined. The N-terminal sequence was homologous to the corresponding portion of the primary structure of horse cytochrome c.