Analysis of the structures of the subunits of the cytochrome bc1 complex from beef heart mitochondria.

The interaction of the protein subunits of the bc1 complex from beef heart is analysed on the basis of protein chemical data and of secondary structure predictions suggesting a large number of amphipathic helices. Electrostatic interactions, i.e. helix-dipole interactions and ionic bonds, may play a major role in the stabilisation of the arrangement of the subunits within the multi-protein complex, formation of subcomplexes and maintenance of the steric strain of cytochrome b. A model of the heme-carrying 'core' of cytochrome b, i.e. of helices II-V, is presented consisting of a twisted '4-alpha-helical' bundle held together by helix-dipole interactions and stabilised by the interaction with other protein subunits of the bc1 complex.