Progress 10/01/04 to 09/30/05
During the past year our group has been very active in understanding the mechanism of nitrogen fixation. We were able to show that different variant enzymes change there ability to be inhibited by CO by simple changes in the amino acids around the FeMo cofactor. This study gives us a strong indication of the regions of the active-site cofactor where substrates and inhibitor bind and how they bind. We have also, for the first time, been able to show the reduction state needed for initial substrate binding prior to reduction. This state occurs two electrons more reduced that the normal as-isolated state of the enzyme. This state, to date, cannot be achieved other than by enzymatic reduction. Therefore, the enzyme must undergo two electron transfer cycles prior to substrate binding.
The resutls from these studies greatly advance our understanding of the mechanism of nitrogen fixation and, with them, add to our abiliy to model nitrogen fixing metal clusters for subsequent non-enzymatic reduction reactions of dinitrogen and similar multipe bonded molecules.
- Variant MoFe Proteins of Azotobacter vinelandii: Effects of Carbon Monoxide on Electron Paramagnetic Resonance Spectra Generated During Enzyme Turnover, Zofia Maskos, Karl Fisher, Morten Sorlie, William Newton and Brian Hales, (2005) J. Biol. Inorg. Chem., 10, 394-406.
- Electron Inventory, Kinetic Assignment (En), Structure, and Bonding of Nitrogenase Turnover Intermediates with C2H2 and CO, Hong-In Lee, Morten Sorlie, Jason Christiansen, Tran-Chin Yang, Junlong Shao, Dennis R. Dean, Brian J. Hales, and Brian Hoffman (2005) J. Amer. Chem. Soc., 127, 15880-15890.