Fine Tuning of Redox Networks on Multiheme Cytochromes from Geobacter sulfurreducens Drives Physiological Electron/Proton Energy Transduction
Electronic distribution scheme for a triheme cytochrome with a proton-linked equilibrium showing the 16 possible microstates. PpcA and PpcD are structurally similar to tetraheme cytochromes , with the exception that heme 2 and the corresponding fragment of the polypeptide chain are absent. Thus, to be consistent with the literature, the heme groups are numbered 1, 3, and 4 according to the order of attachment to the CXXCH motif in the polypeptide chain. The blue and red circles correspond to the protonated and deprotonated microstates, respectively. Hexagons represent heme groups, which can be either reduced (black) or oxidized (white). The microstates are grouped, according to the number of oxidized hemes, in four oxidation stages connected by three one-electron redox steps. and represent the reduced protonated and deprotonated microstates, respectively. and indicate, respectively, the protonated and deprotonated microstates, where i, j, and k represent the heme(s) that are oxidized in that particular microstate.