National Synchrotron Light Source Symposium

Iron containing metalloproteins play key roles in many important biochemical processes. For example, the reduction of dinitrogen to ammonia in biological systems is catalyzed by nitrogenase which is made up of two unique metal clusters, the P-cluster and the FeMo cofactor [1].

Nuclear resonance vibrational spectroscopy (NRVS) is a relatively new technique for understanding iron metalloproteins through their vibrational spectra. It is only sensitive to the vibrations of iron atoms, which gives a useful feature of site selectivity [2].

As part of our program to understand biological nitrogen fixation, we have used NRVS to study simple iron-sulfur cluster containing metalloproteins and nitrogenase [3-4]. Compared to conventional Fe-S clusters, FeMo-cofactor exhibits a strong signal near 190cm-1. This intensity is ascribed to cluster breathing modes whose frequency is raised by an interstitial atom. This work is the first spectroscopic information about the vibrational modes of the intact nitrogenase FeMo-cofactor and P-cluster.

[1] Einsle O et al. (2002) Science, 2002, 297, 1696-1700.
[2] Sturhahn W et al. (1995) Phys. Rev. Lett. 74, 3832-3835
[3] Xiao Y et al. (2006) J. Am. Chem. Soc. 2006, 128, 7608-7612.
[4] Xiao Y et al. (2005) J. Am. Chem. Soc. 2005, 127, 14596-14606.