Subfractionation and characterization of soluble c-type cytochromes from Paracoccus denitrificans cultured under various limiting conditions in the chemostat

Abstract

Soluble c‐type cytochromes were partially purified from Paracoccus denitrificans cells grown in succinate‐ and methanol‐limited aerobic, nitrate‐limited anaerobic and oxygen‐limited chemostat cultures. Five c type could be distinguished with the following apparent molecular masses, absorption maxima and midpoint potentials. (a) 9.2 kDa, 549 nm and +190 mV; (b) 14 kDa, 549 nm and +227 mV; (c) 22 kDa, 552 nm and +190 mV; (d) 30 kDa, 552.7 nm and +160 mV; (e) 45 kDa, a dihaem: 555 nm, +128 mV and 551 nm, ‐163 mV. The 14‐kDa polypeptide was present under all growth conditions examined and most probably is the already well characterized cytochrome c₅₅₀. In methanol‐limited grown cells three additional cytochromes were found, the 9.2‐kDa, 22‐kDa and 30‐kDa ones. Under oxygen‐limited conditions the 45‐kDa and under anaerobic growth conditions small quantities of the 30‐kDa and 45‐kDa cytochromes c were present. Based on the apparent molecular masses the 14‐kDa, 22‐kDa, 30‐kDa and 45‐kDa cytochromes may also be present in membrane‐fractions.