Weiguang Fu

RESONANCE RAMAN STUDIES OF THE 4FE-4S TO 2FE-2S CLUSTER CONVERSION IN THE IRON PROTEIN OF NITROGENASE

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 α,α′‐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.