The cytochrome c domain of dimeric cytochrome cd1 of Paracoccus pantotrophus can be produced at high levels as a monomeric holoprotein using an improved c-type cytochrome expression system in Escherichia coli

Cytochrome cd(1) nitrite reductase from Paracoccus pantotrophus is a dimer; within each monomer there is a largely alpha-helical domain that contains the c-type cytochrome centre. The structure of this domain changes significantly upon reduction of the heme iron, for which the ligands change from His17/ His69 to Met106/His69. Overproduction, using an improved Escherichia coli expression system, of this c-type cytochrome domain as an independent monomer is reported here. The properties of the independent domain are compared with those when it is part of dimeric hole or semi-ape cytochrome cd(1). (C) 2001 Academic Press.