Membrane-associated c-type cytochromes from the green sulfur bacterium Chlorobium limicola forma thiosulfatophilum: Purification and characterization of cytochrome c(553)

Tetraheme cytochromes involved in photosynthetic electron transport have previously been described associated with the reaction centers of purple photosynthetic bacteria; however, similar heme proteins have not until now been characterized in the phylogenetically distinct green sulfur bacteria. In this paper we describe the first isolation and characterization of a multiheme, membrane-associated cytochrome from a green sulfur bacterium, Chlorobium limicola forma thiosulfatophilum. We show that this cytochrome contains a single polypeptide of 32 kDa apparent molecular mass on SDS-PAGE and has a characteristic broad alpha-band absorption at 553 mm. By birth low-temperature absorption and electron paramagnetic resonance spectroscopy, we demonstrate that there are at least four distinct heme groups.