The Roles of Cytochrome c in Membranes of Methylophilus methylotrophus

Biochemistry Department, University of Southampton, Southampton SO9 3TU, UK ABSTRACT Summary: The soluble and membrane-bound cytochromes c of methylotrophic bacteria were investigated in order to determine their relationships with each other, and their roles in electron transport. The proportions of soluble cytochromes cH and cL in various methylotrophs were not markedly dependent on the type of methylotroph nor on conditions of growth. Between 30 and 50% of the cytochrome c of Methylophilus methqdotrophus was bound tightly to membranes; 8% of this was cytochrome cH, 37% was cytochrome cL and 55% was the cytochrome c component of the oxidase, cytochrome co. These cytochromes were purified and characterized. It was concluded that cytochrome cH has no role in the membrane. By contrast, the membrane cytochrome cL has a separate role from that of soluble cytochrome cL; the membrane-bound cytochrome cL may play a role analogous to that of mitochondria1 cytochrome c1 in mediating between cytochrome band the terminal oxidase during the oxidation of NADH.