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

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Abstract
The interaction of the protein subunits of the bc 1 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-α-helical’ bundle held together by helix-dipole interactions and stabilised by the interaction with other protein subunits of the bc 1 complex.