tailieunhanh - Báo cáo Y học: The Fe-only nitrogenase and the Mo nitrogenase from Rhodobacter capsulatus A comparative study on the redox properties of the metal clusters present in the dinitrogenase components

The dinitrogenase component proteins of the conventional Mo nitrogenase (MoFe protein) and of the alternative Fe-only nitrogenase (FeFe protein) were both isolated and purified from Rhodobacter capsulatus, redox-titrated according to the same procedures and subjected to an EPR spectroscopic comparison. In the course of an oxidative titration of the MoFe protein (Rc1Mo) three significant S ¼ 1/2 EPR signals deriving from oxidized states of the P-cluster were detected: (1) a rhombic signal (g ¼ , and ), which showed a bell-shaped redox curve with midpoint potentials (Em) of )195 mV (appearance) and )30 mV (disappearance), (2) an axial signal. | Eur. J. Biochem. 269 1650-1661 2002 FEBS 2002 The Fe-only nitrogenase and the Mo nitrogenase from Rhodobacter capsulatus A comparative study on the redox properties of the metal clusters present in the dinitrogenase components Stefan Siemann Klaus Schneider Melanie Drottboomt and Achim Muller Lehrstuhl fur Anorganische Chemie I Fakultat fur Chemie der Universitat Bielefeld Bielefeld Germany The dinitrogenase component proteins of the conventional Mo nitrogenase MoFe protein and of the alternative Fe-only nitrogenase FeFe protein were both isolated and purihed from Rhodobacter capsulatus redox-titrated according to the same procedures and subjected to an EPR spectroscopic comparison. In the course of an oxidative titration of the MoFe protein Rc1Mo three signihcant S 1 2 EPR signals deriving from oxidized states of the P-cluster were detected 1 a rhombic signal g and which showed a bell-shaped redox curve with midpoint potentials Em of -195 mV appearance and -30 mV disappearance 2 an axial signal g gx with almost identical redox properties and 3 a second rhombic signal g at higher redox potentials 100 mV . While the low-potential rhombic signal and the axial signal have been both attributed to the one-electron-oxidized P-cluster P1 present in two con-formationally different proteins the high-potential rhombic signal has been suggested rather to derive from the P3 state. Upon oxidation the FeFe protein Rc1Fe exibited three signihcant S 1 2 EPR signals as well. However the Rc1Fe signals strongly deviated from the MoFe protein signals suggesting that they cannot simply be assigned to different P-cluster states. a The most prominent feature is an unusually broad signal at g and which proved to be fully reversible and to correlate with catalytic activity. The cluster giving rise to this signal appears to be involved in the transfer of two electrons. The midpoint potentials determined were -80 mV appearance and 70 mV .

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