The 8.5 A projection map of the light-harvesting complex I from Rhodospirillum rubrum reveals a ring composed of 16 subunits.

Abstract
Two‐dimensional crystals from light‐harvesting complex I (LHC I) of the purple non‐sulfur bacterium Rhodospirillum rubrum have been reconstituted from detergent‐solubilized protein complexes. Frozen‐hydrated samples have been analysed by electron microscopy. The crystals diffract beyond 8 A and a projection map was calculated to 8.5 A. The projection map shows 16 subunits in a 116 A diameter ring with a 68 A hole in the centre. These dimensions are sufficient to incorporate a reaction centre in vivo. Within each subunit, density for the alpha‐ and the beta‐polypeptide chains is clearly resolved, and the density for the bacteriochlorophylls can be assigned. The experimentally determined structure contradicts models of the LHC I presented so far.