UM Biophysics Faculty | Roseanne J Sension

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Roseanne J Sension

Biophysical Chemistry, Ultrafast Spectroscopy

Prof. Sension

Associate Professor, Chemistry

Associate Professor, Physics

Ph.D., University of California at Berkeley

Dept:

Office Address: 4529 Chemistry

Phone: (734) 763-6074

Email: rsension@umich.edu

Sension Group Web Site

State-of-the-art femtosecond to nanosecond time-resolved spectroscopic techniques are being used to study reaction mechanism in complicated biological systems. Current projects are focused on investigating the primary charge separation and energy transfer processes in the photosystem II reaction center of green plants, reaction mechanism in B₁₂ dependent enzymes, and the photochemical ring-opening and cis-trans isomerization reactions of provitamin D₃ (7-dehydrocholesterol) and previtamin D₃.

Photosynthetic organisms, both plants and bacteria, store photon energy via charge separation across a membrane. Currently, our group is using femtosecond transient absorption spectroscopy, in conjunction with picosecond fluorescence measurements to unravel the mechanism of primary charge separation in the photosystem II reaction center of plants. Our work on PSII, carried out in collaboration with Professor Yocum, is exploring the charge separation process in a variety of reaction center preparations, differing in the number of proteins, the number of chlorophyll present, and in the preparation protocols.

The second project underway in our group uses time-resolved spectroscopy to study reaction mechanism in B12 dependent enzymes. The key catalytic element in B₁₂ is a unique carbon-cobalt bond. Reactivity in B₁₂ enzymes involves homolysis (adenosylcobalamin dependent enzymes) or heterolysis (methylcobalamin dependent enzymes) of the active carbon-cobalt bond. Although the B₁₂ catalysis is not naturally photoinitiated, a photon can be used to trigger bond homolysis in both enzyme bound and free B₁₂ coenzymes. In addition, protection from photolysis has been proposed as a protein function in B₁₂ systems. The aim of our research program is to use time-resolved spectroscopy to elucidate the role of the protein in controlling and directing the reactivity of the carbon-cobalt bond.

Femtosecond time-resolved deep ultraviolet spectroscopy is being used to investigate polyene photochemistry. Vitamin D3 is produced through ultraviolet photolysis of 7-dehydrocholesterol in the skin. The initial step is the ring-opening reaction of 7-dehydrocholesterol to form previtamin D₃. In our laboratory we have been investigating the photochemical ring opening reaction of both 1,3-cyclohexadiene and the more complicated 7-dehydrocholesterol chromophore.

Ultrafast Spectrscopy of Glutamate Mutase

Representative Publications

Shiang, J. J., Cole, A. G., Sension, R. J., Hang, K., Weng, Y., Trommel, J. S., Marzilli, L. G. and Lian, T., 2006, “Ultrafast Excited State Dynamics in Vitamin B₁₂ and Related Cob(III)alamins” Journal of the American Chemical Society, v128 (3) 801-808.

Sension, R. J., Harris, D. A., and Cole, A. G., 2005 “Time-Resolved Spectroscopic Studies of B₁₂ Coenzymes: A Comparison of the Influence of Solvent on the Primary Photolysis Mechanism and Geminate Recombination of Methyl-, Ethyl-, n-Propyl-, and 5'-Deoxyadenosylcobalamin” Journal of Physical Chemistry B, v109 (46) 21954-21962.

Sension, R. J., Harris, D. A., Stickrath, A. B., Cole, A. G., Fox, C. C., Marsh, E. N. G., 2005 “Time Resolved Measurements of the Photolysis and Recombination of Adenosyl-cobalamin Bound to Glutamate Mutase” Journal of Physical Chemistry B, v109 (38) 18146-18152.

Sension, R.J., Cole, A.G., Harris, A.D., Fox, C.C., Woodbury, N.W., Lin, S., and Marsh. E.N.G., 2004, “Photolysis and Recombination of Adenosylcobalamin Bound to Glutamate Mutase.” Journal of the American Chemical Society, v 126 (6) 1598-1599.

Shiang, J. J., Yoder, L. M., and Sension, R. J. 2003 “Structure and Function in the Isolated Reaction Center Complex of Photosystem II. 2. Models for Energy Relaxation and Charge Separation in a Protein Matrix.” Journal of Physical Chemistry B, v 107 (9) 2162-2169.

Yoder, L. M., Cole, A. G. and Sension, R. J. 2002 “Structure and Function in the Isolated Reaction Center Complex of Photosystem II: Energy and Charge Transfer Dynamics and Mechanism.” Photosynthesis Research v 72 (3) 147-158.

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Biophysics Research Division University of Michigan 4028 Chemistry Building 930 North University Avenue Ann Arbor, MI 48109-1055 UMsitemaker	Phone: (734) 763-6722 Fax: (734) 764-3323 E-mail: biophysics@umich.edu Last Updated: 1/23/2006 © Copyright 2006 University of Michigan