STRUCTURE OF THE LIGHT-HARVESTING ANTENNA FROM RHODOSPIRILLUM-MOLISCHIANUM STUDIED BY ELECTRON-MICROSCOPY

The structure of two types of isolated light-harvesting antenna comple xes from Rhodospirillum molischianum was studied by electron microscop y and image analysis. The B870 reaction center complex forms an almost circular particle with a diameter in the plane of the membrane of abo ut 10.7-11.2 nm. A complex consists of a reaction center surrounded mo st likely by 12 B870 antennae units. An asymmetrical protrusion, consi sting of the cytochrome subunit, gives the reaction center a height of 11.5 nm. The peripheral B800-820 complex is cylindrical, with a diame ter of 5.3 nm and a small central indentation. At low resolution, it i s structurally very similar to the B800-850 complex of Rhodobacter sph aeroides and is considered to be most likely of the alpha(6) beta(6) t ype.