Monday, 23 May 2005
398

This presentation is part of: Spectroscopy of Biomolecules Posters

Trans/Cis Proline Isomerization in Different Solvents Studied by Fluorescence Quenching due to Intramolecular Electron Transfer

Youssef Issa, David S. Talaga, Edward W. Castner, and Stephan S. Isied. Rutgers University, Piscataway, NJ

The factors that control the slow (t1/2 ~ seconds) trans- to cis- proline isomerization in peptides and proteins continue to attract significant attention because of the involvement of proline residues in a diverse number of protein conformational processes. The Polyproline II (trans) structure is favored in high polarity solvents where as the Polyproline I (cis) structure is favored in solvents of low polarity. We report here on a series of donor acceptor proline peptides with one and two amino acid residues derivatized with the fluorophore, tetramethylrhodamine (TMR) at the N-terminus and dimethyl-1,4-phenelenediamine (DMPD), at the C-terminus. This series of molecules is soluble in solvents ranging from hexane to water. A sensitive method to evaluate the amount of trans/cis conformers in this series at low concentrations is using Time Correlated Single Photon Counting (TSCPC) by monitoring intramolecular electron transfer from the DMPD (electron donor) to the 1S state of TMR (electron acceptor) . The fluorescence quenching of TMR in these derivatives was monitored over a broad range of solvent polarity. It was observed that the lifetimes of both the MonoPro and the Dipro residues decreases with decreasing solvent polarity with lifetimes for DiPro ranging between 2.0 ns (water) to 0.08 ns (hexane). The decrease in lifetimes follow the increasing amounts of the cis proline conformation at lower solvent polarity, where the electron donor and acceptor are in close proximity. Analysis of these lifetimes in terms of solvent effects on driving force, reorganization energy, and proline conformations will be discussed. .

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