“…Cytochrome b 5 is an electron-transfer protein that is widely distributed in nature. The structure±function relationship of cytochrome b 5 has been studied based on the crystal structures of mutants of cytochrome b 5 , the microsomal cytochrome b 5 and the outer mitochondrial membrane cytochrome b 5 (Funk et al, 1990;Rivera et al, 1998;Xue et al, 1999;Wu et al, 2000Wu et al, , 2002Gan et al, 2002;Wang, Wu et al, 2002;Yao et al, 2002;Cowley et al, 2002;Ren et al, 2004).…”