We have studied the temperature dependence of the IR stretch bands of carbon monoxide (CO) in the Xe 4 internal cavity of myoglobin mutant L29W-S108L at cryogenic temperatures. Pronounced changes of band areas and positions were analyzed quantitatively by using a simple dynamic model in which CO rotation in the cavity is constrained by a static potential. The librational dynamics of the CO causes a decrease of the total spectral area. A strong local electric field splits the CO stretch absorption into a doublet, indicating that CO can assume opposite orientations in the cavity. With increasing temperature, the two peaks approach each other, because the average angle of the CO with respect to the electric field increases. A combined classical and quantum-mechanical analysis precisely reproduces the observed temperature dependencies of both spectral area and peak shifts. It yields the height of the energy barrier between the two wells associated with opposite CO orientations, V 0 Ϸ 2 kJ͞mol, and the frequency of oscillation within a well, Ϸ 25 cm ؊1 . The electric field in the protein cavity was estimated as 10 MV͞cm.E ven the simplest biological reactions exhibit a stunning level of complexity when studied in detail (1). The traditional chemical description in terms of transitions between a few discrete molecular species can only be a coarse approximation, because biological macromolecules are exceedingly complex physical systems that can assume a multitude of conformations (conformational substates) with markedly different structural and kinetic properties (2).Ligand binding in myoglobin (Mb), a small heme protein in mammalian muscle, has served for a long time as a biological model reaction. Pioneering low-temperature flash photolysis studies of CO and O 2 binding to Mb by Frauenfelder and coworkers (3) in the 70s gave clear evidence of protein structural heterogeneity as well as multiple intermediate states along the reaction pathway. Only in recent years have structural details of these intermediates become available. Fig. 1 shows a sketch of the free-energy surface governing ligand binding and a model of the active site of carboxymyoglobin (MbCO) (mutant L29W). After photodissociation, the CO moves from the bound-state location A to docking site B on top of the heme group. This primary photoproduct has been characterized by x-ray cryocrystallography of photolyzed MbCO crystals at 20-40 K (4-6). Fourier transform IR (FTIR) spectroscopy shows two distinct stretch bands for CO in state B (7, 8) that originate from two opposite orientations of the CO dipole with respect to an internal electric field. Recent femtosecond IR experiments (8) and time-resolved x-ray structure determinations (9) at room temperature have confirmed the relevance of docking site B in physiological ligand binding.Sites A and B are not the only internal locations available to ligands. Cryocrystallographic studies (10-12) have shown that, under proper illumination conditions, ligands can be chased into more remote, secondary docking sites C...

IrisFP is a photoactivatable fluorescent protein that combines irreversible photoconversion from a green- to a red-emitting form with reversible photoswitching between a fluorescent and a nonfluorescent state in both forms. Here we introduce a monomeric variant, mIrisFP, and demonstrate how its multiple photoactivation modes can be used for pulse-chase experiments combined with subdiffraction-resolution imaging in living cells by using dual-color photoactivation localization microscopy (PALM).

PET/MRI of patients with head and neck cancer yielded good diagnostic capability, similar to PET/CT. Further studies on larger cohorts to prove these first results seem justified.

We report on lasing in rhodamine 6G-doped, conical polymeric microcavities with high quality factors fabricated on a silicon substrate. Threshold pump energies as low as 3 nJ are achieved by free-space excitation in the quasistationary pumping regime with lasing wavelengths around 600 nm. Finite element simulations confirm that lasing occurs in whispering gallery modes which corresponds well to the measured multimode laser-emission. The effect of dye concentration on lasing threshold and lasing wavelength is investigated and can be explained using a standard dye laser model.

This paper presents a stochastic model to forecast the German population and labor supply until 2060. Within a cohort-component approach, our population forecast applies principal components analysis to birth, mortality, emigration, and immigration rates, which allows for the reduction of dimensionality and accounts for correlation of the rates. Labor force participation rates are estimated by means of an econometric time series approach. All time series are forecast by stochastic simulation using the bootstrap method. As our model also distinguishes between German and foreign nationals, different developments in fertility, migration, and labor participation could be predicted. The results show that even rising birth rates and high levels of immigration cannot break the basic demographic trend in the long run. An important finding from an endogenous modeling of emigration rates is that high net migration in the long run will be difficult to achieve. Our stochastic perspective suggests therefore a high probability of substantially decreasing the labor supply in Germany.