Bulletin of the American Physical Society
2005 72nd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 10–12, 2005; Gainesville, FL
Session NC: Biophysics II |
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Chair: Steve Hagen, University of Florida Room: Hilton Azalea |
Saturday, November 12, 2005 10:45AM - 10:57AM |
NC.00001: Modeling Electric Fields of Peripheral Nerve Block Needles. James Ch. Davis, Norman E. Anderson, Mark W. Meisel, Jason G. Ramirez, F. Kayser Enneking Peripheral nerve blocks present an alternative to general anesthesia in certain surgical procedures and a means of acute pain relief through continuous blockades. They have been shown to decrease the incidence of postoperative nausea and vomiting, reduce oral narcotic side effects, and improve sleep quality. Injecting needles, which carry small stimulating currents, are often used to aid in locating the target nerve bundle. With this technique, muscle responses indicate needle proximity to the corresponding nerve bundle. Failure rates in first injection attempts prompted our study of electric field distributions. Finite difference methods were used to solve for the electric fields generated by two widely used needles. Differences in geometry between needles are seen to effect changes in electric field and current distributions. Further investigations may suggest needle modifications that result in a reduction of initial probing failures. [Preview Abstract] |
Saturday, November 12, 2005 10:57AM - 11:09AM |
NC.00002: Mechanism of folding/unfolding of Rd-apocyt $b_{562}$: a molecular dynamics simulation study Harianto Tjong, Huan-Xiang Zhou The four-helix bundle protein Rd-apocyt $b_{562}$, a redesigned stable variant of apocytochrome$ b_{562}$, has been shown to exhibit two-state folding kinetics. Its transition-state ensemble has been characterized by \textit{$\Phi $}-value analysis and native-state hydrogen exchange. To elucidate the molecular basis of the transition-state ensemble, we have carried out high-temperature molecular dynamics simulations of the unfolding process. In agreement with experiment, helix one was found to melt first, followed by helix four, and then by helices three and two. This ordering among the four helices could be rationalized by differences in helix propensities and by the presence of tertiary contacts. [Preview Abstract] |
Saturday, November 12, 2005 11:09AM - 11:21AM |
NC.00003: Biophysical analysis of swimming force by \textit{Chlamydomonas} flagella John N. Yukich, Karen K. Bernd, Rachel Patton McCord Numerous studies have used indirect techniques to investigate the function of flagella of the unicellular green algae \textit{Chlamydomonas reinhardtii}. We report the first direct measurement of the flagellar swimming force of \textit{Chlamydomonas}. Using an optical trap we detect a 75{\%} decrease in swimming force between wild type cells and mutant cells lacking an internal flagellar component. This difference is consistent with previous estimates. To examine flagellar organization and function, we deflagellated cells and examined force generation during flagellar regrowth.~ As expected, fully regrown flagella are functionally equivalent to flagella of untreated wild type cells.~ However, analysis of swimming force vs. flagella length reveals intriguing patterns where increases in force do not always correspond with increases in length. These investigations of flagellar force contribute to the understanding of \textit{Chlamydomonas }motility and demonstrate the advantages of the optical trapping technique in studies of cell motility. [Preview Abstract] |
Saturday, November 12, 2005 11:21AM - 11:33AM |
NC.00004: Evidence for a Border-Collision Bifurcation in Paced Cardiac Tissue Carolyn Berger, Hana Dobrovolny, David G. Schaeffer, Wanda Krassowska, Daniel J. Gauthier Bifurcations in the electrical response of cardiac tissue can destabilize spatial-temporal waves of electrical activity in the heart, leading to tachycardia or even fibrillation. Therefore, it is important to characterize the types of bifurcations occurring in cardiac tissue. Our goal is to classify the bifurcation that occurs in cardiac cells when a change in pacing rate induces a transition from 1:1 to 2:2 phase-locked behavior. Current mathematical models predict that the bifurcation mediating the transition is a supercritical pitchfork type. For such a bifurcation, small random noise is predicted to be amplified by greater amounts as the bifurcation is approached (Weisenfeld). However, our experimental observations of paced bullfrog myocardium driven by small beat-to-beat alternations in the pacing rate (rather than driven by noise) displays de-amplification as the bifurcation is approached. To explain this surprising result, we hypothesize that the transition to 2:2 behavior is mediated by border-collision bifurcation, which is predicted to show little noise amplification. Wiesenfeld, K. Phys. Rev. A \textbf{32}, 1744 (1985). [Preview Abstract] |
Saturday, November 12, 2005 11:33AM - 11:45AM |
NC.00005: Evanescent Wave Excitation and Raman Spectroscopy of Bacteriorhodopsin on Gallium Nitride Waveguides Alfred Keller, Yu Guo, Sonya Ortiz, April Pope, Heidi Hockel, Eric Johnson, Leonid Chernyak, Alfons Schulte Waveguides fabricated by nano-lithography can serve as substrates for thin protein films. In the composite structure the waveguide provides the guiding layer, and the thin film is the material whose Raman spectrum is desired. The top molecular layer is accessible through the decaying evanescent field of a mode propagating in the waveguide. Thin layers of bacteriorhodopsin were deposited on GaN waveguides created by standard lithography and inductively coupled etching processes. A 488 nm beam from an Argon ion laser was coupled into the gallium nitride waveguide and the evanescent field was employed to initiate the photocycle and excite Raman scattering in the bacteriorhodopsin film. Under stationary conditions the Raman spectrum in the fingerprint region shows the presence of the light-adapted state and the M intermediate. This suggests that the protein is in its native state and that optical switching of bacteriorhodopsin can be achieved and probed by evanescent wave excitation. [Preview Abstract] |
Saturday, November 12, 2005 11:45AM - 11:57AM |
NC.00006: Application of a cooled-ccd astronomy camera to biological imaging Annie Guzzi, William Hammond, Paulo Garcia, Robert Welsh, Jianguo Qian, Eric Bradley, Margaret Saha A cooled-ccd digital camera (Santa Barbara Instrument Group ST-6) originally intended for astronomical observation has been modified for use in fluorescent/luminescent imaging for biological studies. Enhanced cooling techniques to achieve low-noise conditions and typical applications in biological work will be described. [Preview Abstract] |
Saturday, November 12, 2005 11:57AM - 12:09PM |
NC.00007: Application of fluorescent ``Quantum Dots" to biological imaging Paulo Garcia, Annie Guzzi, William Hammond, Robert Welsh, Jianguo Qian, Eric Bradley, Margaret Saha We have carried out tests to obtain reliable fluorescent images in mice with an economical, modified digital imager. Procedures used and images obtained using small dielectric spheres (``qdots''; Quantum Dot Corporation) in both normal and nude mice are described. [Preview Abstract] |
Saturday, November 12, 2005 12:09PM - 12:21PM |
NC.00008: Electrostatic enhancement of protein-protein association rate predicted from a transition-state model. Ramzi AlSallaq, Huan-Xiang Zhou Protein-protein association is central to most protein functions. The rate of association is limited by the translational and rotational diffusion that brings the two proteins into their bound configuration. Electrostatic interactions between the protein partners can enhance an otherwise low rate resulting from the stereospecificity of the association. Based on the idea that the asynchronous decrease in translational/rotational entropy and the free energy of interactions leads to a free-energy barrier, a transition-state theory for association has been proposed [Vijayakumar et al. (J. Mol. Biol, 1998); Zhou (Biopolymers, 2001)]. Here we further develop and test this theory. The model for the transition state is built from the dependence of native contacts on translation/rotational degrees of freedom. The predicted electrostatic rate enhancement is found to agree well with experimental data for the effects of ionic strength and charge mutations on the association of barnase and barstar. [Preview Abstract] |
Saturday, November 12, 2005 12:21PM - 12:33PM |
NC.00009: Electrical Detection of Immobilized Proteins With Ungated AlGaN/GaN High Electron Mobility Transistors. Byoung Sam Kang, Fan Ren, Lin Wang, Charles Lofton, Weihong Tan, Stephen Pearton, A. Dabiran, A. Osinsky, P. Chow Ungated AlGaN/GaN High Electron Mobility Transistor structures were functionalized in the gate region with aminopropyl silane. This serves as a binding layer to the AlGaN surface for attachment of fluorescent biological probes. Fluorescence microscopy shows that the chemical treatment creates sites for specific absorption of probes. Biotin was then added to the functionalized surface to bind with high affinity to streptavidin proteins. The HEMT drain-source current showed a clear decrease of 4 uA as this protein was introduced to the surface, showing the promise of this all-electronic detection approach for biological sensing. [Preview Abstract] |
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