Figure 8. Comparison of the structures of cytochrome c1 and cytochrome c (stereo pair). Above is a ribbon diagram of mitochondrial cytochrome c in a standard orientation with the open C corner of the heme facing the viewer, and the heme propionates directed downward. Below is cytochrome c₁, rotated to put the common features between the two cytochromes in the same orientation. Corresponding segments of each cytochrome are drawn with the same color. Helices labeled a1, a3, and a5 correspond to similarly labeled helices in cytochrome c. The N- and C- termini are labeled in cytochrome c₁.