The long-range goal of the proposed research is better understanding of structures and mechanisms of metal-containing enzymes. We have chosen a number of Ni, Fe, V/Mo, and Mn systems where soft x-ray spectroscopy and x-ray magnetic circular dichroism (XMCD) have special strengths for answering the important issues. As needed, we will also use EXAFS and FT-IR spectroscopy. Our emphasis will be issues of electronic structure and catalytic mechanism that are difficult to address by crystallography. Towards this end, we will also explore cryogenic and photochemical approaches to sample preparation. The general hypotheses to be tested include: [1.] Is the conversion between high-spin and low-spin Ni(II) species important for the reactivity of Ni enzymes. To what extent is the redox activity Ni-based, and when is it more appropriate to describe the electronic changes as centered on the ligands? How does the distribution of spin density compare with the distribution of electron density? What are the structures and activation mechanisms for catalytically inactive precursor forms of Ni enzymes? When is Ni involved in substrate binding, and when is it a 'spectator'? What are the roles of Cu and Zn in these enzymes? [2.] During nitrogen fixation, are V/Mo present as 'spectators' to modulate the catalytic activity of the Fe, or are the key substrate reactions on V/Mo? Are V/Mo magnetically coupled to the rest of the M-center? [3.] How does the electron density change on Mn throughout the catalytic cycle of photosystem ll? How do inhibitors such as F- bind, and how does this change in different S-states? Although the focus of our experiments is primarily at the electronic and molecular level, it is also important to understand the cellular distribution of these trace metals. Recent advances in soft x-ray microscopy allow x-ray tomographic analysis at the 500 A scale. We propose to exploit our knowledge of metalloenzyme soft x-ray spectroscopy to record images that are selective for Fe or Ni. In order to conduct better x-ray experiments, we will make improvements to existing equipment and also develop some new instrumentation. We will build a small cryostat with differential pumping, so that soft x-ray experiments no longer require UHV. We will also fabricate a 36-element contiguous STJ detector for fluorescence detected x-ray absorption measurements.

Agency
National Institute of Health (NIH)
Institute
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Type
Research Project (R01)
Project #
5R01EB001962-15
Application #
7216243
Study Section
Metallobiochemistry Study Section (BMT)
Program Officer
Lopez, Hector
Project Start
1990-04-01
Project End
2010-02-28
Budget Start
2007-03-01
Budget End
2010-02-28
Support Year
15
Fiscal Year
2007
Total Cost
$176,510
Indirect Cost
Name
University of California Davis
Department
Miscellaneous
Type
Schools of Engineering
DUNS #
047120084
City
Davis
State
CA
Country
United States
Zip Code
95618
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Pushkar, Yulia; Long, Xi; Glatzel, Pieter et al. (2010) Direct detection of oxygen ligation to the Mn(4)Ca cluster of photosystem II by X-ray emission spectroscopy. Angew Chem Int Ed Engl 49:800-3
George, S J; Webb, S M; Abraham, J L et al. (2010) Synchrotron X-ray analyses demonstrate phosphate-bound gadolinium in skin in nephrogenic systemic fibrosis. Br J Dermatol 163:1077-81
Delfino, Ines; Cerullo, Giulio; Cannistraro, Salvatore et al. (2010) Observation of terahertz vibrations in the nitrogenase FeMo cofactor by femtosecond pump-probe spectroscopy. Angew Chem Int Ed Engl 49:3912-5

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