Biomedical subjects
Publications and source records attributed to Douwe A Wiersma.
We demonstrate that the value of the underlying frequency-frequency correlation function can be retrieved from a two-dimensional optical correlation spectrum through a simple relationship. The proposed method yields both intuitive clues and a quantitative measure of the dynamics of the system. The technique is applied to studying the effects of temperature and phase changes on liquid-glass solvent dynamics.
We show how cross-phase modulation between two pulses, combined with optimal pulse shaping at the input of a dielectric medium, can be used to generate nearly single-cycle pulses that are tunable from the ultraviolet to the mid-infrared at the output of the medium, precompensating for dispersion to all orders.
Bacteriorhodopsin is a proton-transporting membrane protein in Halophilic archaea, and it is considered a prototype of membrane transporters and a model for G-protein-coupled receptors. Oligomerization of the protein has been reported, but it is unknown whether this feature is correlated with, for instance, light activation. Here, we have addressed this issue by reconstituting bacteriorhodopsin into giant unilamellar vesicles. The dynamics of the fully active protein was investigated using fluorescence correlation spectroscopy and freeze fracture electron microscopy. At low protein-to-lipid ratios (<1:10 w/w), a decrease in mobility was observed upon protein photoactivation. This process occurred on a second time scale and was fully reversible, i.e. when the dark-adapted state was reestablished the lateral diffusion rate of the protein was returned to that prior to activation. A similar decrease in lateral mobility as observed upon photoactivation was obtained when bacteriorhodopsin was reconstituted at high protein-to-lipid ratios (>1:10 w/w). We interpret the shifts in mobility during light adaptation as being caused by transient photoinduced oligomerization of bacteriorhodopsin. These observations are fully supported by freeze-fracture electron microscopy, and the size of the clusters during photoactivation was estimated to consist of two or three trimers.