%0 Journal Article %J Biophysical Journal %D 2008 %T Terahertz spectroscopy of bacteriorhodopsin and rhodopsin: Similarities and differences %A Balu, R. %A Zhang, H. %A Zukowski, E. %A Chen, J. Y. %A Markelz, A. G. %A Gregurick, S. K. %K Biophysics %K bovine rhodopsin %K conformational-changes %K elastic %K frequency normal-modes %K light activation %K molecular-dynamics simulation %K neutron-scattering %K protein-coupled receptors %K transmembrane helices %K vibrational-modes %K wild-type %X

We studied the low-frequency terahertz spectroscopy of two photoactive protein systems, rhodopsin and bacteriorhodopsin, as a means to characterize collective low-frequency motions in helical transmembrane proteins. From this work, we found that the nature of the vibrational motions activated by terahertz radiation is surprisingly similar between these two structurally similar proteins. Specifically, at the lowest frequencies probed, the cytoplasmic loop regions of the proteins are highly active; and at the higher terahertz frequencies studied, the extracellular loop regions of the protein systems become vibrationally activated. In the case of bacteriorhodopsin, the calculated terahertz spectra are compared with the experimental terahertz signature. This work illustrates the importance of terahertz spectroscopy to identify vibrational degrees of freedom which correlate to known conformational changes in these proteins.

%B Biophysical Journal %V 94 %P 3217-3226 %8 Apr %@ 0006-3495 %G English %9 Article %M WOS:000254420100030 %R 10.1529/biophysj.107.105163 %0 Journal Article %J Applied Physics Letters %D 2007 %T Terahertz dielectric assay of solution phase protein binding %A Chen, J. Y. %A Knab, J. R. %A Ye, S. J. %A He, Y. F. %A Markelz, A. G. %K dynamics %K lysozyme %K Physics %K spectroscopy %K water %X

The authors demonstrate a method for rapid determination of protein-ligand binding on solution phase samples using terahertz dielectric spectroscopy. Measurements were performed using terahertz time domain spectroscopy on aqueous solutions below the liquid-solid transition for water. Small ligand binding sensitivity was demonstrated using triacetylglucosamine and hen egg white lysozyme with a decrease in dielectric response with binding. The magnitude of the change increases with frequency. (c) 2007 American Institute of Physics.

%B Applied Physics Letters %V 90 %P 3 %8 Jun %@ 0003-6951 %G English %9 Article %M WOS:000247305400108 %] 243901 %! Appl. Phys. Lett.Appl. Phys. Lett. %R 10.1063/1.2748852 %0 Journal Article %J Applied Physics Letters %D 2006 %T Terahertz transmission characteristics of high-mobility GaAs and InAs two-dimensional-electron-gas systems %A Kabir, N. A. %A Yoon, Y. %A Knab, J. R. %A Chen, J. Y. %A Markelz, A. G. %A Reno, J. L. %A Sadofyev, Y. %A Johnson, S. %A Zhang, Y. H. %A Bird, J. P. %K field-effect transistors %K photoconductivity %K Physics %K plasma-waves %K radiation %K resonant detection %K subterahertz %X

Frequency-dependent complex conductivity of high-mobility GaAs and InAs two-dimensional-electron-gas (2DEG) systems is studied by terahertz time domain spectroscopy. Determining the momentum relaxation time from a Drude model, the authors find a lower value than that from dc measurements, particularly at high frequencies/low temperatures. These deviations are consistent with the ratio tau(t)/tau(q,) where tau(q) is the full scattering time. This suggests that small-angle scattering leads to weaker heating of 2DEGs at low temperatures than expected from dc mobilit9y. (c) 2006 American Institute of Physics.

%B Applied Physics Letters %V 89 %P 3 %8 Sep %@ 0003-6951 %G English %9 Article %M WOS:000240875800066 %] 132109 %! Appl. Phys. Lett.Appl. Phys. Lett. %R 10.1063/1.2357605