Structure, Function, and Evolution of Eukaryotic and Prokaryotic Respiratory Electron Transfer Systems

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1) Bovine heart mitochondrial complex III (bc_1 was prepared by an improved method. This preparation showed a ping-pong mechanism analyzed by a steady-state reaction kinetics, when it transfers electrons from QH_2 to cytochrome c.2) This bc_1 complex was reproducibly crystallized in a large scale to reddish parallelpipe forms by treating the preparation with polyethyleneglycol containing sucrose within 1-2 weeks at room temperature.3) The crystal diffracted X-ray at less than 8 A resolution, but it was rather fragile for mechanical shocks and unstable by exposing it to air. Therefore, some improvements in crystallization and manipulations to X-ray analysis.4) Euglena cytochrome c was found to be stable if it was prepared in the reduced form, promisingit to be a good preparation for crystallization.5) The base sequence of cDNA encoding Euglena cytochrome c_1 was completed. The comparison of various c_1 sequences revealed that His and Met were the ligands to the heme iron atom. Heme C was bound to only one cysteine through a thioether bond and Phe was in the position of Cys usually binding the heme together with the other.6) The site directed mutations of putative heme ligands, His and Met, in yeast cytochrome c_1 showed that these two have important roles for the iron chelation and assembly of the bc_1 complex.7) One of the two acidic regions supposed to interact with cytochrome c at around position 70 in yeast cytochrome c_1 was found to be not essential for the interaction by gene deletion experiments.8) Sequence analyses of 13kDa(two different polypeptides), 2okDa, and 20kDa Sub-units revealed that there are several regions forming iron-sulfur clusters in mitochondrial Complex I.9) A cyanobacterial b_6f complex was found to be able to transfer electrons to cytochrome aa_3 through cytochrome c_<553>.