EPR study of 1Asp-3Cys ligated 4Fe-4S iron-sulfur cluster in NB-protein (BchN-BchB) of a dark-operative protochlorophyllide reductase complex |
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| Authors: | Kondo Toru Nomata Jiro Fujita Yuichi Itoh Shigeru |
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| Affiliation: | aDivision of Material Science (Physics), Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan;bGraduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan;cChemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226-8503, Japan;dPresto, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan |
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| Abstract: | Dark-operative protochlorophyllide oxidoreductase, a nitrogenase-like enzyme, contains two [4Fe–4S] clusters, one in the L-protein ((BchL)2) and the other in the NB-protein ((BchN–BchB)2). The reduced NB-cluster in the NB-protein, which is ligated by 1Asp/3Cys residues, showed a broad S = 3/2 electron paramagnetic resonance signal that is rather rare in [4Fe–4S] clusters. A 4Cys-ligated NB-cluster in the mutated variant BchB–D36C protein, in which the Asp36 was replaced by a Cys, gave a rhombic normal S = 1/2 signal and lost the catalytic activity. The results suggest that Asp36 contributes to the low redox potential necessary to reduce protochlorophyllide. |
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| Keywords: | Abbreviations: EPR, electron paramagnetic resonance DPOR, dark-operative protochlorophyllide oxidoreductase LPOR, light-dependent protochlorophyllide oxidoreductase Pchlide, Protochlorophyllide Chl, chlorophyll BChl, Bacteriochlorophyll |
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