Hi,
Below there is an article which gives the structure of cytochrome bc1 I think it may help you.
When the structure of DNA was revealed by Watson and Crick in 1953, nobody could have predicted that, a generation and a half later, we would have the sorts of genetic Engineering that is now commonplace. The structure of cytochrome bc1, revealed in July by Bing Jap, may not be as fruitful, but it is still extremely promising. The cytochrome is found in mitochondria, the organelles often called the powerhouses of the cell, where most food is broken down into smaller energy units, but the structure of this molecule may provide a key to treating Alzheimer disease or any of a number of other degenerative diseases - including aging.
The report reveals the crystal structure of the molecule, also known as complex III, which plays a critical role in the relay of electrons for energy production. It is one of four protein complexes in the mitochondrial respiratory chain. The solution took some eight years, and used x-ray crystallography to produce structural images of the entire 11 subunits of cytochrome bc1 at a resolution of approximately 3 angstroms, using cytochrome bc1 from cow heart cells.
Every plant and animal cell contains hundreds of mitochondria, which generate about 90% of the energy the cell needs. The energy is generated by the transfer of electrons from food molecules. The electrons are passed through the respiratory chain and into the production of ATP, adenosine triphosphate. If anything interferes with the electron transfer process, energy production drops away, which is not good for the maintenance of normal life. Aside from anything else, the drop-off also leads to the production of oxygen free-radical molecules which can cause mutations in DNA, both in the mitochondria and also in the nucleus.
Cytochrome bc1 is revealed as a dimer, a complex of two molecular chains called monomers. These monomers determine the shape of the dimer, and in particular, of a hollow between the two monomers, and the shape of the dimer controls the operation of the cytochrome. With the structure revealed, the hollow, previously no better than a hypothesis, is now confirmed.
In living mitochondria, the dimer is a non-crystalline protein embedded in the lipids of the mitochondrial inner membrane, so the first challenge was to crystallise the protein, because x-ray crystallography (as its name implies) depends on the existence of a crystal. The first step was to break the membrane up by using just the right amount of just the right detergent.
The small complex II protein and the very large complex I protein remain to be solved, and Jap and his colleagues will now join the effort, already under way, to solve complex I, using a combination of x-ray and electron crystallography techniques. Jap describes this as involving "multiple crystal averaging and phase information from both heavy atom derivatives and electron micrographs".
