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Abstract The crystal structure analysis of tuna heart cytochrome c has been carried out at 2.45 A resolution using three isomorphous heavy atom derivatives. The space group of P21212 contrasts with the P43 of oxidized cytochrome c. Changes in conformation are seen near the heme crevice and on the right side of the molecule. The entire molecule in the reduced state is more compact and more closed to its surroundings. The heme group moves slightly within its protein framework. A mechanism for reduction is proposed based on orientations of aromatic groups and on recent chemical modification studies. The over-all chain folding is observed to be very similar in mammalian-type cytochrome c and in c-type cytochromes from two bacteria.
Takano et al. (Wed,) studied this question.