A unique photosynthetic reaction center from Heliobacterium chlorum

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Abstract
A 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.