Emeritus Professor - -Biophysical -- Les & Dot Broussard Alumni Association Departmental Professor
Bachelor's Degree(s): Carnegie Institute of Technology, 1966
PhD: University of Minnesota, 1970 Post Doc: Royal Institution of Great Britian, 1970-71
PostDoc: Northwestern University, 1971-73
Phone: (225) 578-4694
Fax: (225) 578-3458
Office: 327 Choppin Hall
Area of Interest
Trace metals have been known for a long time to play many important roles in biology. Our research investigates one of these roles, that being the function of redox active metals and metal clusters in proteins. Metalloproteins constitute some of the most important enzymes known to man. Many of these enzymes are involved with the fundamental reactions needed for life on this planet, and the metal clusters are often the active site. Currently we are investigating the mechanism of one of the most important enzymes in Nature, nitrogenase, which catalyzes the fixation or reduction of N2 into ammonia:
N2 + 6H+ + 6e- i 2NH3
We have used a combination of techniques to probe this mechanism, including those involved with molecular biology, enzymology and spectroscopy. Two recent examples best illustrate the wealth of information that can be obtained.
Carbon monoxide is a potent inhibitor of the nitrogenase reaction. In the presence of CO two different EPR signals are generate, one at low pressure (lo-CO, PCO = 0.05 atm) and the second at high pressure (hi-CO, PCO = 0.5 atm). These signals are only generated during enzymatic turnover and thus represent intermediate states of catalysis. Using both EPR and ENDOR (electron nuclear double resonance) spectroscopic techniques along with 13C labeled CO and 57Fe label enzyme, we were able to demonstrate that the lo-CO and hi-CO EPR signals arose from CO binding (1 and 2 CO’s, respectively) to FeMo cofactor center of the enzyme. We further revealed that the single CO in lo-CO bound to the cofactor in a bridging fashion while both CO’s in hi-CO exhibited terminal binding.
In a related recent study we were able to detect an acetylene adduct binding to the active site during acetylene reduction by nitrogenase. Again, using isotopic labeling (13C and 2H) we demonstrated that this intermediate was a reduced acetylene molecule (C2H2) bridging Fe atoms in the waist region of the FeMo cofactor (see figure) prior to subsequent release and protonation to form ethylene.
Two views of acetylene bridging across two Fe atoms in the FeMo-cofactor.
These results are extremely significant because the represent the first detection of intermediate states of nitrogenase catalysis. We recently expanded our spectroscopic capabilities and are now employing the techniques of MCD (magnetic circular dichroism) spectroscopy and XAS (x-ray absorption spectroscopy, utilizing the LSU CAMD facility) to more completely elucidate the structure of the different intermediate states of nitrogenase as well as other enzymatic reactions.
Awards & Honors
Chair, 2002 Gordon Conference on Nitrogen Fixation, 2002
NIH Biophysical A Study Section, 2001
NIH Special Study Section Reviewer, 1999
Grant Review Panel Member, 1998
Working Group on Hazardous Waste Disposal, 1998
Zofia Maskos and Brian J. Hales. Photo Lability of CO Bound to the Cofactor of Mo-nitrogenase from Azotobacker vinelandii. Journal of Inorganic Biochemistry, 2003, 93, 11-17
- Sorlie, J. Christiansen, B.J. Lemon, J. Peters, D.R. Dean and B. Hales. Mechanistic Features and Structure of the Nitrogenase MoFe a-Gln195 Protein. Biochemistry, 2001, 40, 1540-1459
- Lee, M. Sorlie, J. Christiansen, R. Song, D.R. Dean, B.J. Hales and B. Hoffman. Characterization of an Intermediate in the Reduction of Acetylene by the Nitrogenase a-Gln195 MoFe Protein by Q-band EPR and 13C and 1H ENDOR. J. Amer. Chem. Soc., 2000, 122, 5582-5587
- Sorlie, J. Christiansen, D.R. Dean and B.J. Hales. Detection of a New Radical and FeMo-Cofactor EPR Signal During Acetylene Reduction by the a-H195Q Mutant of Nitrogenase. J. Amer. Chem. Sco., 1999, 121, 9457-9458
Former Ph.D. Students
|Anupam Gupta PhD,Bell Labs
Karen Howard PhD,Procter & Gamble
Melinda Oliver PhD,
Ronald Tittsworth PhD,LSU CAMD
Carol Blanchard PhD,Postdoc
Linda Cameron PhD,Postdoc