Isolation and characterization of a noval membrane-bound cytochrome <TEX>$C_{553}$</TEX> from the strictly anaerobic phototroph, heliobacillus mobilis

Heliobacillus mobilis is a strictly anaerobic Gram-positive bacterium which contains a primitive Photosystem I-type reaction center. The membrane-bound cytochrome <TEX>$C_{553}$</TEX> from the heliobacterium suggested to be the immediate electron donor to the photooxidized pigment (P798+) has been isolated and characterized. The heme protein was visualized as a major component with an apparent molecular size of 17kDa in TMBZ-staining analysis of the membrane preparation and showed characteristic <TEX>$alpha$</TEX> (552.5 nm), <TEX>$eta$</TEX> (522nm), and Soret absorption (416 nm) peaks of a typical reduced c-type cytochrome in the partially purified sample. The internal 43 amino acid sequence of the electron donor was obtained by chemical agent and protease treatments followed by N-terminal sequencing of the resulting fragments. The internal sequence carries lots of lysine residues and a Cys-X-X-Cys-His sequence motif which are the characteristics of typical c-type cytochromes. The analysis of the sequence by FAST or FASTA program, however, did not show any significant similarity to other known heme proteins.