Selenol binds to iron in nitrogenase iron-molybdenum cofactor: An extended x-ray absorption fine structure study

Journal Article · Mon Feb 14 23:00:00 EST 1994 · Proceedings of the National Academy of Sciences of the United States of America

DOI:https://doi.org/10.1073/pnas.91.4.1290· OSTI ID:255158

Conradson, S D; Hodgson, K O; Hedman, B ^[1]; Burgess, B K ^[2]; Newton, W E ^[3]; Cicco, A Di ^[4]; Filipponi, A ^[5]; Wu, Z Y; Natoli, C R ^[6]

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1. Stanford Univ., CA (United States)
2. Univ. of California, Irvine, CA (United States)
3. Virginia Polytechnic Institute and State Univ., Blacksburg, VA (United States)
4. Universita degli Studi di Camerino, Camerino (Italy)
5. Universita degli Studi dell`Aquila (Italy)
6. Istituto Nazionale di Fisica Nucleare, Frascati (Italy)

The biological N{sub 2}-fixation reaction is catalyzed by the enzyme nitrogenase. The metal cluster active site of this enzyme, the iron-molybdenum cofactor (FeMoco), can be studied either while bound within the MoFe protein component of nitrogenase or after it has ben extracted into N-methylformamide. The two species are similar but not identical. For example, the addition of thiophenol or selenophenol to isolated FeMoco causes its rather broad S = 3/2 electron paramagnetic resonance signal to sharpen and more closely approach the signal exhibited by protein-bound FeMoco. The nature of this thiol/selenol binding site has been investigated by using Se-K edge extended x-ray absorption fine structure (EXAFS) to study selenophenol ligated to FeMoco, and the results are reported here. EXAFS data analysis at the ligand Se-K edge was performed with a set of software, GNXAS, that provides for direct calculation of the theoretical EXAFS signals and least-squares fits to the experimental data. Data analysis results show definitively that the selenol (and by inference thiol) binds to Fe at a distance of 2.4 {angstrom}. In contrast, unacceptable fits are obtained with either Mo or S as the liganded atom (instead of Fe). These results provide quantitative details about an exchangeable thio/selenol binding site on FeMoco in its isolated, solution state and establish an Fe atom as the site of this reaction. Furthermore, the utility of ligand-based EXAFS as a probe of coordination in polynuclear metal clusters is demonstrated.

• Sponsoring Organization: USDOE
• OSTI ID: 255158
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 4 Vol. 91; ISSN PNASA6; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ABSORPTION SPECTROSCOPY
CHEMICAL BONDS
MOLECULAR STRUCTURE
NITROGENASE
SELENIUM
X RADIATION