Fig. 20.5 Superposition of the folded structures of the three cytochrome C proteins from Fig. 20.5 based on a ribbon model: Paracoccus denitrificans in blue, Rhodospirillum rubrum in red, and tuna fish in yellow (left). The cytochromes bind via a histidine and a methionine to an iron–heme center. The structures were determined by X-ray crystallography. Structural deviations occur particularly in the loop regions. On the right side the same superposition is shown, only here the individual amino acids are color-coded. The same colors in all three ribbon models show identical amino acids at different positions (color coding: Ala: light gray, Val: chartreuse, Gly: white: Ile: bright green, Leu: olive green, Pro: pink, Phe: violet, Tyr: dark purple, Trp: light violet, Asp: dark red, Glu: wine red, Asn: turquoise, Gln: cyan, Lys: blue, His: light blue, Arg: medium blue, Ser: light orange, Thr: dark orange, Cys: light yellow, Met: dark yellow.