Characterization of cytochrome c₈ isoform newly purified from the purple bacterium, Rubrivivax gelatinosus

Abstract

The cytochrome c₈ isoform, was newly isolated from purple photosynthetic bacterium Rubrivivax gelatinosus mutant lacking HiPIP and high- and low-potential cytochromes c₈. The isocyt c₈ has an approximately 10 kDa molecular mass and the about +280 mV redox midpoint potential. Absorption spectrum of the reduced form showed the α-band at 552 nm. Flash-induced kinetic measurements using the isocyt c₈ and the photosynthetic membrane indicated that the isocyt c₈ has a functional ability of an electron donor to the RC-bound cytochrome subunit. The primary structure of the isocyt c₈, determined by peptide sequencing followed by cloning and nucleotide sequencing, showed 65 % amino acid sequence identity with the known high-potential cytochrome c₈ of R. gelatinosus. The gene arrangement suggested participation of the two high-potential cytochromes c₈ to nitrite reduction.