Resonance Raman studies of the [4Fe-4S] to [2Fe-2S] cluster conversion in the iron protein of nitrogenase |
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Authors: | W G Fu T V Morgan L E Mortenson M K Johnson |
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Institution: | Center for Metalloenzyme Studies, University of Georgia, Athens 30602. |
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Abstract: | Resonance Raman spectroscopy has been used to investigate the Fe-S stretching modes of the 4Fe-4S]2+ cluster in the oxidized iron protein of Clostridium pasteurianum nitrogenase. The results are consistent with a cubane 4Fe-4S] cluster having effective Td symmetry with cysteinyl coordination for each iron. In accord with previous optical and EPR studies (1984) Biochemistry 23, 2118-2122], treatment with the iron chelator alpha, alpha'-dipyridyl in the presence of MgATP is shown to effect cluster conversion to a 2Fe-2S]2+ cluster. Resonance Raman data also indicate that partial conversion to a 2Fe-2S]2+ cluster is induced by thionine-oxidation in the presence of MgATP in the absence of an iron chelator. This result suggests new explanations for the dramatic change in the CD spectrum that accompanies MgATP-binding to the oxidized Fe protein and the anomalous resonance Raman spectra of thionine-oxidized Clostridium pasteurianum bidirectional hydrogenase. |
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