Characterization of a Blue Copper Protein Auracyanin from the Filamentous Anoxygenic Phototroph Roseiflexus castenholzii

Abstract

Filamentous anoxygenic phototrophic bacteria (formerly called green non-sulfur bacteria) are positioned in the most deeply branched lineage among phototrophic bacteria in the 16S rRNA phylogenetic tree. They have a quinone-type reaction center complex which is similar to that of purple photosynthetic bacteria. However, other components working in the photosynthetic electron transfer pathway of the filamentous bacteria have not been fully clarified. In this study we purified and characterized the candidate protein, auracyanin, from Roseiflexus castenholzii. The purified auracyanin showed a typical absorption spectrum of a blue-copper protein and had a midpoint potential of 236mV. We are also trying to purify the possible quinol oxidoreductase in the filamentous anoxygenic phototroph.