... in the wild-type PA c-551 and itsquintuple mutant. The mutated residues in the quintuple mutant, and the corresponding ones of the wild-type PA c-551 and HT c-552 are coloredpurple, green, and ... attached to the polypeptide chain via twothioether bonds, formed from the vinyl groups of the heme and the two cysteine residues in the consensus Cys-X-X-Cys-His motif [1–4]. Site-directed mutagenesis ... those of the 82-amino-acidcytochrome c-551 from a mesophile, Pseudomonas aerugi-nosa (PA c-551). Comparisons of the two proteins indicatedthat the amino-acid residues are 56% identical [5], and...