Structure of the light harvesting antenna from Rhodospirillum molischianum studied by electron microscopy

Abstract The structure of two types of isolated light-harvesting antenna complexes from Rhodospirillum molischianum was studied by electron microscopy and image analysis. The B870 reaction center complex forms an almost circular particle with a diameter in the plane of the membrane of about 10.7–11.2 nm. A complex consists of a reaction center surrounded most likely by 12 B870 antennae units. An asymmetrical protrusion, consisting of the cytochrome subunit, gives the reaction center a height of 11.5 nm. The peripheral B800–820 complex is cylindrical, with a diameter of 5.3 nm and a small central indentation. At low resolution, it is structurally very similar to the B800–850 complex of Rhodobacter sphaeroides and is considered to be most likely of the α 6 β 6 type.