Membrane-bound cytochromes c of Pseudomonas aeruginosa grown aerobically. Purification and characterization of cytochromes c-551 and c-555.

Membrane-bound cytochromes c of Pseudomonas aeruginosa grown aerobically were investigated. By detecting polypeptides with heme-catalyzing peroxidase activity on a sodium dodecyl sulfate polyacrylamide gel, four major (Band I, 33,000 daltons; II, 25,000; III, 20,000; IV, 16,000) and one minor (V, 11,500) hemoproteins were found in the membrane fraction, while one hemoprotein (VI, 8,200) was detected in a small amount in the cytosol fraction. All these hemoproteins (bands I to VI) appeared to be cytochromes c, because all bands were detected even after being treated with HCl-acetone. Of the membrane-bound cytochromes c, cytochromes c-551 (band IV) and c-555 (band V) were solubilized with Triton X-100 and purified by repeated DEAE-cellulose column chromatography. Both purified cytochromes c-551 and c-555 were monomeric and their molecular weights were estimated to be 16,400 and 11,500, respectively. Their respective midpoint potentials were 0.31 and 0.34 V, and their respective isoelectric points in the reduced form were 3.8 and 5.2. The purified cytochromes c-551 and c-555 were found to be clearly different from "soluble" cytochrome c-551, and might function in the membrane-bound aerobic respiratory chain of P. aeruginosa.