NMR-Based amide hydrogen-deuterium exchange measurements for complex membrane proteins: development and critical evaluation

A method for measuring site-specific amide hydrogen-deuterium exchange rates for membrane proteins in bilayers is reported and evaluated. This method represents an adaptation and extension of the approach of Dempsey and co-workers (Biophys. J. 70, 1777-1788 (1996)) and is based on reconstituting (15)N-labeled membrane proteins into phospholipid bilayers, followed by lyophilization and rehydration with D(2)O or H(2)O (control). Following incubation for a time t under hydrated conditions, samples are again lyophilized and then solubilized in an organic solvent system, where (1)H-(15)N HSQC spectra are recorded. Comparison of spectra from D(2)O-exposed samples to spectra from control samples yields the extent of the H-D exchange which occurred in the bilayers during time t. Measurements are site specific if specific (15)N labeling is used. The first part of this paper deals with the search for a suitable solvent system in which to solubilize complex membrane proteins in an amide "exchange-trapped" form for NMR quantitation of amide peak intensities. The second portion of the paper documents application of the overall procedure to measuring site-specific amide exchange rates in diacylglycerol kinase, a representative integral membrane protein. Both the potential usefulness and the significant limitations of the new method are documented.     

200GeV AuAu碰撞中前快度区的微分椭圆流

Identified particle elliptic flow results are presented for the Au+Au reaction at s_NN=200GeV as a function of transverse momentum and pseudorapidity. Data at pseudorapidities η≈0,1, and 3.4 were obtained using the two BRAHMS spectrometers. Differential v₂ (η,p_t) values for a given particle type are found to be essentially constant over the covered pseudorapidity range, in contrast to the integral v₂ values which have previously been observed to decrease at forward rapidities. A softening of the particle spectra at forward angles is found to account for at least part of the integral v₂ falloff. The data are found to be consistent with existing constituent quark scaling systematics.     

Aluminium

Ohne Zusammenfassung     

Manipulations of listeners' echo perception are reflected in event-related potentials

To gain information from complex auditory scenes, it is necessary to determine which of the many loudness, pitch, and timbre changes originate from a single source. Grouping sound into sources based on spatial information is complicated by reverberant energy bouncing off multiple surfaces and reaching the ears from directions other than the source's location. The ability to localize sounds despite these echoes has been explored with the precedence effect: Identical sounds presented from two locations with a short stimulus onset asynchrony (e.g., 1-5 ms) are perceived as a single source with a location dominated by the lead sound. Importantly, echo thresholds, the shortest onset asynchrony at which a listener reports hearing the lag sound as a separate source about half of the time, can be manipulated by presenting sound pairs in contexts. Event-related brain potentials elicited by physically identical sounds in contexts that resulted in listeners reporting either one or two sources were compared. Sound pairs perceived as two sources elicited a larger anterior negativity 100-250 ms after onset, previously termed the object-related negativity, and a larger posterior positivity 250-500 ms. These results indicate that the models of room acoustics listeners form based on recent experience with the spatiotemporal properties of sound modulate perceptual as well as later higher-level processing.     

Determining the optimum wavelength pairs to use for molecular absorption thermometry based on the continuous-spectral lower-state energy

A novel technique for selecting wavelengths that optimize the temperature precision of absorption-based thermometry is developed. A single universal objective function considering continuous spectral lower-state energy , spectral absorbance intensities and an experimental noise level is derived and applied in a brute-force approach to analyze two-wavelength, Doppler-broadened H₂O vapor-absorbance thermometry in the 1.33-1.37 μm range. The results reveal the top wavelength pairs and their temperature precisions over a wide temperature range from 280 to 2800 K. Although the spectral database used includes over thousands of transitions in this spectral range, the top pairs are composed of only 12 unique wavelengths. This wavelength selection technique is able to help researchers choose key wavelengths that will perform well in practical applications.     

Objectively discerning Autler-Townes splitting from electromagnetically induced transparency

Autler-Townes splitting (ATS) and electromagnetically induced transparency (EIT) both yield transparency in an absorption profile, but only EIT yields strong transparency for a weak pump field due to Fano interference. Empirically discriminating EIT from ATS is important but so far has been subjective. We introduce an objective method, based on Akaike's information criterion, to test ATS vs EIT from experimental data for three-level atomic systems and determine which pertains. We apply our method to a recently reported induced-transparency experiment in superconducting-circuit quantum electrodynamics.     

Efficient algorithm for optimizing adaptive quantum metrology processes

Quantum-enhanced metrology infers an unknown quantity with accuracy beyond the standard quantum limit (SQL). Feedback-based metrological techniques are promising for beating the SQL but devising the feedback procedures is difficult and inefficient. Here we introduce an efficient self-learning swarm-intelligence algorithm for devising feedback-based quantum metrological procedures. Our algorithm can be trained with simulated or real-world trials and accommodates experimental imperfections, losses, and decoherence.     

Sorption of CO2, C2H4, N2O and their binary mixtures in poly(methyl methacrylate)

Sorption of carbon dioxide, ethylene, and nitrous oxide in poly(methyl methacrylate) (PMMA) at 35°C has been characterized for each gas as a pure component and for mixtures of carbon dioxide/ethylene and carbon dioxide/nitrous oxide. Pressures up to 20 atm were examined. Pure-component sorption isotherms are concave to the pressure axis for each of the gases. This behavior is accurately described by the dual-mode sorption model. Using only the purecomponent dual-mode parameters and the generalization of the model for gas mixtures, one can predict the total concentration of gas sorbed in the polymer to within an average deviation of ±2.01% for the CO₂/C₂H₄/PMMA system and ±0.98% for the CO₂/N₂O/PMMA system. In both systems, for each component of the mixture, sorption levels were lower than corresponding pure-component sorption levels at pressures equal to the partial pressure of the respective components in the mixture. Depression of the sorbed concentration in mixture situations appears to be a general feature of the above systems and can be substantial in some situations. For the CO₂/C₂H₄/PMMA system, use of pure-component sorption data to estimate the total sorbed concentration in the mixture would be in error by as much as 40% if one failed to account for competition phenomena responsible for depression in mixed-gas situations. Mixture pressures as high as 20 atm were studied for both systems and in the CO₂/N₂O/PMMA system sorbed concentrations reach 33.90 [cm³(STP)/cm³ polymer] without any significant deviation from model predictions.     

Muscle spindles are concentrated in the superior vocalis subcompartment of the human thyroarytenoid muscle

It is hypothesized that different parts of the thyroarytenoid muscle (TA) are functionally specialized. Specifically, the TA is divided into a lateral muscularis compartment and a medial vocalis compartment. This study examined the distribution of muscle spindles throughout the human TA as an indicator of these functional differences. Histological cross-sections from the anterior, middle, and posterior regions of five human membranous vocal folds were examined for the number and location of muscle spindles. There was an average of 6.1 muscle spindles in sections from each region with no significant variation between the different regions (p < .05). However, in sections from all three regions, the muscle spindles were always found to be concentrated in the superior medial quadrant of the TA (mean 85.9%, p < .01). The inferior medial, superior lateral, and inferior lateral quadrants of the TA contained 11.96%, 2.17%, and 0%, respectively, of the total muscle spindles. Within the superior medial quadrant, most of the muscle spindles were localized in the most superficial part of the muscle.The results of this study demonstrate that the majority of TA muscle spindlesare concentrated in its superior medial quadrant, an area we have termed the superior vocalis subcompartment (SC. This finding suggests that the superior vocalis SC is functionally distinct from the remainder of the TA. It is hypothesized that tension in the superior vocalis SC can be controlled independently from the remainder of the TA, and this capability is used to effect the biomechanics of vocal fold vibration during phonation.