Structural studies of the molybdenum site in the MoFe protein and it FeMo cofactor by EXAFS
Nitrogenase is a complex bacterial enzyme system that is responsible for the conversion of atmospheric N/sub 2/ to ammonia. The structure and function of molybdenum in the MoFe protein of this system has been the subject of a number of investigations, including the use of X-ray absorption spectroscopy. This paper reports the results of the authors recent studies on several states of the MoFe protein and its FeMo cofactor (which is extruded by treatment with N-methylformamide). Mo K-edge (XANES) and extended fine structure (EXAFS) spectra have been recorded to high energies above the absorption edge with excellent signal-to-nose on the semireduced form of the MoFe protein from both Clostridium pasteurianum and Azotobacter vinelandii and on the as isolated FeMo-co and FeMo-co treated with benzenethiol and with benzeneselenol. In all of the states studied, EXAFS results reveal that the Mo is in an environment that contains two or three oxygen (or nitrogen) atoms at 2.10-2.12 A, three to five S atoms at 2.37 A, and three to four Fe atoms at 2.68-2.70 A. The numbers of these ligands change upon removal of the cofactor from the protein as discussed in the paper. For FeMo-co, comparisons also show that thil/selenol is not binding directly to the Mo site. The results of these EXAFS (and their XANES published earlier) definitely show the presence of several low-Z ligands and are not compatible with a tetrahedral arrangement of only nearest S neighbors at the Mo site.
- Research Organization:
- Stanford, Univ., CA
- OSTI ID:
- 5654174
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 109:24
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
10 SYNTHETIC FUELS
AMMONIA
CHEMICAL PREPARATION
IRON COMPOUNDS
FINE STRUCTURE
MOLECULAR STRUCTURE
MOLYBDENUM COMPOUNDS
EXPERIMENTAL DATA
NITROGEN
NITROGENASE
X RADIATION
DATA
ELECTROMAGNETIC RADIATION
ELEMENTS
ENZYMES
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
IONIZING RADIATIONS
NITRO-GROUP DEHYDROGENASES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
NUMERICAL DATA
OXIDOREDUCTASES
RADIATIONS
REFRACTORY METAL COMPOUNDS
SYNTHESIS
TRANSITION ELEMENT COMPOUNDS
550200* - Biochemistry
090320 - Inorganic Hydrogen Compound Fuels- Preparation- (1976-1989)