Abstract
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.
Highlights
The crystal structure analysis of tuna heart cytochrome c has been carried out at 2.45 A resolution using three isomorphous heavy atom derivatives
This isomorphism does not extend to t,he reduced protein
Reduced bonito cytochrome crystallizes in orthorhombic space group I’212121 (16), tuna crystallizes in space group P21212, and we have been unable to induce reduced horse cytochrome to produce large enough crystals to measure by x-ray methods
Summary
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 l’t, and IIg sites were rclated to a common origin by means of a Fourier difference map using protein signs obtained from the platinum derivative, and structure amplitude changes, A8’, from the mercury. Difference Fourier maps for all three derivatives are shown for illustrative purposes, in each case using phases (signs) obtained from the two derivatives other than the one whose heavy atom sites are depicted.
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