3-DIMENSIONAL STRUCTURE OF BOVINE CYTOCHROME-BC(1) COMPLEX BY ELECTRON CRYOMICROSCOPY AND HELICAL IMAGE-RECONSTRUCTION

Cytochrome bc(1) complex from bovine heart has been reconstituted into tubular crystals, The three-dimensional structure of the complex in l ipid bilayer has been obtained at an effective resolution of 16 Angstr om by electron cryomicroscopy and helical image reconstruction, The co mplex is in a dimeric form, in which the monomers are associated close ly in extramembrane domains on both sides of the membrane, The large i nner domain is distinctively hollow and the small outer domain consist s of a flat mass and two bulbous extrusions. These domains are connect ed by two narrow transmembrane columns. Locations of the subunits and the redox centres in the model are proposed.