Crevice-opened conformer

The pH dependence of cytochrome c oxidation-reduction reactions and the studies of modified cytochrome c thus demonstrate that the coordination environment of the iron and the conformation of the protein are relatively labile and strongly influence the reactivity of the metallo-protein toward oxidation and reduction. The effects seen may originate chiefly from alterations in the thermodynamic barriers to electron transfer, but the conformation changes are expected to affect the intrinsic barriers also. One such conformation change is the opening of the heme crevice referred to above. The anation and Cr(II) reduction studies provide an estimate of 60 sec 1 for this process in Hh(III) at 25°C (59). To date, no evidence has been found for a rapid heme-crevice opening step in ferrocytochrome c. 

TFIIS binding, (NTP entry, RNA exit during backtracking and arrest) TFIIS binding, crevice opening triggers conformational changes... 

An interesting parallel was drawn between the N -> / equilibrium and the open-crevice-closed-crevice equilibrium of cytochrome c. Spectroscopic evidence had indicated that the heme iron was buried in a crevice and to account for its reactivity with ligands, conformational motility was proposed between a nonreactive closed... 

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