A unique photosynthetic reaction center from Heliobacterium chlorum

AbstractA previously unknown type of photosynthetic reaction center in the brownish-green bacterium Heliobacterium chlorum is described. The reaction center is tightly bound in a highly proteinaceous undifferentiated plasma membrane and contains bacteriochlorophyll g, which has major in vivo absorbancies at 788, 576 and 370 nm. The purified membrane shows a reversible photobleaching at 798 nm; the reaction center bacteriochlorophyll g is designated P798. A reversible photobleaching at 553 nm is assigned to photooxidation of a membrane-bound c-type cytochrome. The membrane structure, pigment composition and photochemical properties suggest that H. chlorum may represent a fifth family of anoxygenic photosynthetic procaryotes