Three-Dimensional Structure of the Protein Portion

FIGURE 4. The Co- back bone trace of a dimer of bovine heart cytochrome c oxidase, (left) A view to the transmembrane surface and (right) a view from the cytosolic side. 

A concave surface which is created by subunits II, Via and VIb on the intermembrane side of subunit I, is about 25 in diameter, suggesting that it is the binding site for cytochrome c. The transmembrane a-helices of the nuclear encoded subunits form helix-helix interactions with any one pair of these helices crossing at one of three inclination angles of approximately O, 20 and 50, which provide the most stable mode of interaction. Thus, the nuclear-encoded subunits along with their transmembrane helices contribute to the overall stability of the enzyme. This contribution is an example of one of the possible physiological roles provided by these subunits. 

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