Figure 5. Model of wild-type human mitochondrial cytochrome b (green) superimposed on a model of F181L mutant (cyan). The side chain conformation of Phe181 and Arg177 (green) in the wild-type and Leu181 and Arg177 (cyan) in the mutant has been represented in the ball and stick. The conformation of the Arg177 side chain is different in the native and mutant protein. The Arg side chain in the wild-type adopts an orientation to minimize the repulsive force with Phe181.