Lance C. SeefeldtLance C. Seefeldt

Professor
Biochemistry
B.S., 1983, University of Redlands, California
Ph.D., 1989, University of California, Riverside
Postdoctoral, 1989-93, University of Georgia
435.797.3964 seefeldt@cc.usu.edu
web page

Our laboratory is using multidisciplinary approaches including molecular biology, biochemistry, and biophysics to elucidate a molecular understanding of the mechanism of the metalloenzyme nitrogenase.

Nitrogenase is the enzyme responsible for all biological nitrogen fixation, a central reaction in the global nitrogen cycle. The reduction of N2 to NH3 catalyzed by nitrogenase can be summarized by the
equation:

N2 + 8 H+ + 8 e- +16 MgATP —> 2 NH3 + H2 + 16 MgATP + 16 Pi

Biological nitrogen fixation accounts for approximately 80 % of the total input of fixed nitrogen into the biosphere each year (in excess of 2 x 1014 grams/year) and thus is essential to all living systems.

Given the significance of the reaction catalyzed by nitrogenase, there is considerable interest in understanding how the enzyme works. Nitrogenase is a complex metalloproteins that contains three different metal-based centers. A general diagram of the participation of the two nitrogenase proteins, ATP, electrons, and the metal centers is shown in the scheme.

We are working towards providing answers to four outstanding questions regarding how nitrogenase works: 1) How does N2 bind to the nitrogenase active site, 2) How are electrons delivered to the active site for N2 reduction, 3) What are the roles for MgATP hydrolysis in the reaction, and 4) How are the unusual metal centers of nitrogenase biosynthesized. To gain answers to these questions, we are employing a range of approaches including site-directed mutagenesis, EPR, rapid kinetics, NMR, CD, and x-ray spectroscopy. Students working in the group gain first hand training in these and other methods that are ideal for pursuing jobs in industry or academics.

NONE

Selected Publications

Barney, B.M.; Lukoyanov, D.; Yang, T.C.; Dean, D.R.; Hoffman, B.M.; Seefeldt, L.C. “A methyldiazene (HN=N-CH3)-derived species bound to the nitrogenase active site FeMo-cofactor: implications for mechanism,”  Proc. Nat. Acad. Sci. USA, 2006 (in press).

Barney, B.M.; Yang, T.C.; Igarashi, R.Y.; Dos Santos, P.C.; Laryukhin, M.; Lee, H.I.; Hoffman,B.M.; Dean, D.R.; Seefeldt, L.C., “Intermediates trapped during nitrogenase reduction of N≡N, CH3-N=NH, and H2N-NH2,” J. Am. Chem. Soc. 127, 2005, 14960-14961.

Yang, T.C.; Maeser, N.K.; Laryukhin, M.; Lee, H.I.; Dean, D.R.; Seefeldt, L.C.; Hoffman, B.M., “The interstitial atom of the nitrogenase FeMo-cofactor:  ENDOR and ESEEM evidence that it is not a nitrogen,” J. Am. Chem. Soc.  127, 2005, 12804-12805.

Barney, B.M.; Laryukhin, M.; Igarashi, R.Y.; Lee, H.I.; Dos Santos, P.C.; Yang, T.C.; Hoffman,B.M.; Dean, D.R.; Seefeldt, L.C., “Trapping a hydrazine reduction intermediate on thenitrogenase active site,” Biochemistry 44, 2005, 8030-8037.

Igarashi, R.Y.; Laryukhin, M.; Dos Santos, P.C.; Lee, H.I.; Dean, D.R.; Seefeldt, L.C.; Hoffman, B.M., “Trapping H- bound to the nitrogenase FeMo-cofactor active site during H2 evolution:  Characterization by ENDOR spectroscop,”J. Am. Chem. Soc. 127, 2005, 6231-6241.