Characterization of two inducible periplasmic c-type cytochromes from Paracoccus denitrificans

When grown on methanol or methylamine, Paracoccus denitrificans synthesized three periplasmic soluble c-type cytochromes, cytochrome c550 and two additional cytochromes which were not present during growth on succinate and have not previously been characterized. These cytochromes have been separated from each other and their physical properties have been determined. The inducible cytochromes, c551i and c553i, exhibit Mr and pI values of 22,000 and 3.5, and 30,000 and 3.8, respectively. Cytochrome c553i binds CO. None of these cytochromes accepted electrons directly from methylamine dehydrogenase, but each accepted electrons from amicyanin, the electron acceptor for methylamine dehydrogenase. Cytochrome c551i was the most efficient electron acceptor for amicyanin, exhibiting a half-time of reaction at least 6 and 15 times faster than those observed for cytochromes c553i and c550, respectively.