Figure 3.

Kinetic square-scheme for conformationally-gated ET between iso-1-Cytc and small inorganic reagents in the reduced, A_Red, and oxidized, A_Ox, states. Iso-1-Cytc can be in either its native state with Met80 bound to the heme or in an alkaline conformer with an alternate ligand, L, bound to the heme. L is either His79 or Lys73 in the current work. In Path A, the Fe³⁺-heme alkaline conformer is reduced first to the Fe²⁺-heme alkaline conformer and then switches the His79 or Lys73 heme ligand for Met80 to form the native conformational state. The reduction of the oxidized alkaline conformer is controlled by the bimolecular rate constants k_ET(Alk) and k_−ET(Alk). The rate constant for converting the reduced alkaline conformer to the reduced native conformer is k_b′ and for converting the reduced native conformer to the reduced alkaline conformer is k_f′. In Path B, gated ET, the Fe³⁺-heme alkaline conformer first exchanges its ligand to reach the Fe³⁺-heme native conformer before it is reduced. The rate constant for converting the oxidized alkaline conformer to the oxidized native conformer is k_b and for converting the oxidized native conformer to the oxidized alkaline conformer is k_f. (This assignment of k_f and k_b matches that typically used with the alkaline conformational transition of Cytc.) The reduction of the oxidized native conformer is controlled by the bimolecular rate constants k_ET and k_−ET. This figure is adapted from reference 14.