%0 Journal Article %J Biophysical Journal %D 2020 %T Evidence of Intramolecular Structural Stabilization in Light Activated State of Orange Carotenoid Protein %A McKinney, J. A. %A Sharma, A. %A Crossen, K. %A Deng, Y. %A George, D. K. %A Lechno-Yossef, S. %A Kerfeld, C. %A Markelz, A. G. %K Biophysics %X

Orange carotenoid protein (OCP) controls efficiency of the light harvesting antenna, the phycobilisome (PBS), in diverse cyanobacteria and prevents oxidative damage. It is the only known photoactive protein that uses a carotenoid, canthaxanthin, as its chromophore. The structure of OCP consists of two globular domains, connected by an unstructured loop, that forms a hydrophobic pocket for the carotenoid. In low light, canthaxanthin bound OCP is inactive and appears orange. Illumination by strong light results in an active state that interacts with the PBS to induce fluorescence quenching, a red appearance and conformational changes that include a 12Å shift by canthaxanthin into the N-terminal domain. Terahertz (THz) dynamical transition measurements and anisotropic terahertz microscopy are used to measure the intramolecular structural dynamics in the inactive and active states, which can be induced by photoexcitation or chaotropic salts. The measurements indicate that the active state has a decrease in structural flexibility, which may be related to enhanced interactions with the PBS.

%B Biophysical Journal %V 118 %P 208A-208A %8 Feb %@ 0006-3495 %G English %N 3 %9 Meeting Abstract %M WOS:000513023201290 %R 10.1016/j.bpj.2019.11.1245 %0 Journal Article %J Biophysical Journal %D 2017 %T Escaping the Water Cage: Protein Intramolecular Vibrations and the Dynamical Transition %A Xu, M. Y. %A Niessen, K. A. %A Deng, Y. T. %A Michki, N. S. %A Markelz, A. G. %K Biophysics %B Biophysical Journal %V 112 %P 318A-318A %8 Feb %@ 0006-3495 %G English %9 Meeting Abstract %M WOS:000402375600574 %R 10.1016/j.bpj.2016.11.1723 %0 Journal Article %J Semiconductor Science and Technology %D 1994 %T ENERGY RELAXATION AT THZ FREQUENCIES IN ALXGA1-XAS HETEROSTRUCTURES %A Asmar, N. G. %A Markelz, A. G. %A Gwinn, E. G. %A Hopkins, P. F. %A Gossard, A. C. %X

We report 4.2 K studies of the dependence of the in-plane, DC conductivity of a quasi 2D electron gas on the amplitude E(omega) of applied fields with frequencies from 0.25 THz to 3.5 THz. We analyse the dependence of sigma(DC) on E(omega) assuming that electron-optical phonon scattering dominates energy relaxation, that the absorbed power has a Drude form and that the electron distribution is thermal. This simple analysis is self-consistent: Arrhenius plots of the estimated energy loss rate have a slope near -homega(LO)BAR/k(B) for all frequencies, as expected for energy loss by optical phonon emission. We find that the effective energy relaxation time tau(epsilon) varies with the frequency of the applied field, from tau(epsilon) approximately 4 ps at 0.34 THz to tau(epsilon) approximately 0.3 ps at 3.45 THz. This may indicate a frequency-dependent form for the hot-phonon distribution.

%B Semiconductor Science and Technology %V 9 %P 828-830 %8 May %@ 0268-1242 %G eng %M WOS:A1994NM75300116 %! Semicond. Sci. Technol. %R 10.1088/0268-1242/9/5S/116