| Co-Investigator(Kenkyū-buntansha) |
TANI Fumito Kyushu University, Institute for Materials Chemistry and Engineering, Associate Professor, 先導物質化学研究所, 助教授 (80281195)
SHIMAZAKI Yuichi Kyushu University, Institute for Materials Chemistry and Engineering, Research Associate, 先導物質化学研究所, 助手 (80335992)
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| Research Abstract |
Cytochrome c oxidase (CcO) is known to be a family of enzymes, which metabolite dioxygen to water by an efficient four-electron reduction pathway with concomitant translocation of proton through membranes in mitochondria. The enzyme contains heme(hemea_3), (his)_3Cu(Cu_B), and His-cross linked Tyr at the active site. The exact functions, however, of these components as well as its dioxygen reduction mechanism. The enzyme is also interested on the similarity of its reaction with one at the O2 electrode of a fuel cell. Thus, the
We first examined the preparation of heme-Cu complexes and tried to clarify their reactivity with O_2 as well as the structure of the resultant peroxy complexes. Tris(pyridylmethyl)amine-tethered iron porphyrin was reacted with O2 to give the corresponding peroxo complex in a quite high stability. We obtained its single crystals and its X-ray crystallographic analysis showed the peroxo complex taking μ-η^2:η^1 structure. This was the first example of the structura
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l determination of hetero-dimetallic peroxo complexes. Howerver, the peroxo complexes were stable and only showed gradual decomposition to the corresponding μ-oxo one.
In order to simulate the dioxygen reaction at the enzyme, the remaining residues, Tyr-His and His as an axial ligand to heme a_3, are considered to be important. We have prepared an elaborate model, which bears all components at the CcO active site. This model exhibited an interesting reaction : First, it gave the corresponding peroxo complex [Fe^<III>-O_2-Cu^<II>], possibly μ-1,2 form, at a low temperature. It was gradually converted to the superoxy one [Fe^<III>-O_2・/Cu^I], where the Cu ion was Cu^I. Since peroxy-to-superoxy transformation has never been reported so far, this is a new reaction. This reaction partly simulates the early stage one of O_2 reaction in the enzyme. Thus, the Tyr group in the Tyr-His crosslink could play an important role for stabilization of the superoxy complex in the enzyme as a H+ donor. The success of the O2 complex at the accurate active site model opens the new way to clarify its further reaction. Less
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