X-ray Dose (x-ray + dose)

Distribution by Scientific Domains

Selected Abstracts

Radiation damage of protein crystals at cryogenic temperatures between 40,K and 150,K

Tsu-Yi Teng
X-ray radiation damage of lysozyme single crystals by an intense monochromatic beam from the Advanced Photon Source is studied at cryogenic temperatures between 40,K and 150,K. The results confirm that primary radiation damage is both linearly dependent on the X-ray dose and independent of temperature. The upper limit for the primary radiation damage observed in our previous study [Teng & Moffat (2000), J. Synchrotron Rad. 7, 313317] holds over the wider temperature range of this study. The X-ray diffraction quality of the data acquired at 40,K is superior to those at 100,K, apparently due to temperature dependence of secondary and tertiary radiation damage and to reduced thermal motion. [source]

Optimization of data collection taking radiation damage into account

Gleb P. Bourenkov
To take into account the effects of radiation damage, new algorithms for the optimization of data-collection strategies have been implemented in the software package BEST. The intensity variation related to radiation damage is approximated by log-linear functions of resolution and cumulative X-ray dose. Based on an accurate prediction of the basic characteristics of data yet to be collected, BEST establishes objective relationships between the accessible data completeness, resolution and signal-to-noise statistics that can be achieved in an experiment and designs an optimal plan for data collection. [source]

The interdependence of wavelength, redundancy and dose in sulfur SAD experiments

Michele Cianci
In the last decade, the popularity of sulfur SAD anomalous dispersion experiments has spread rapidly among synchrotron users as a quick and streamlined way of solving the phase problem in macromolecular crystallography. On beamline 10 at SRS (Daresbury Laboratory, UK), a versatile design has allowed test data sets to be collected at six wavelengths between 0.979 and 2.290, in order to evaluate the importance and the interdependence of experimental variables such as the Bijvoet ratio, wavelength, resolution limit, data redundancy and absorbed X-ray dose in the sample per data set. All the samples used in the experiments were high-quality hen egg-white lysozyme crystals. X-radiation damage was found to affect disulfide bridges after the crystals had been given a total dose of 0.20 107,Gy. However, with such a total dose, it was still possible in all cases to find a strategy to collect data sets to determine the sulfur substructure and produce good-quality phases by choosing an optimum combination of wavelength, exposure time and redundancy. A ,|,ano|/,(,ano), greater than 1.5 for all resolution shells was a necessary requirement for successful sulfur SAD substructure location. Provided this is achieved, it seems possible to find an optimum compromise between wavelength, redundancy and dose to provide phasing information. The choice of the wavelength should then follow the sample composition and the diffracting properties of the crystal. For strongly diffracting crystals, wavelengths equal or shorter than 1.540, can be selected to capture the available data (provided the Bijvoet ratio is reasonable), while a longer wavelength, to gain as high a Bijvoet ratio as possible, must be used for more weakly diffracting crystals. These results suggest that an approach to a sulfur SAD experiment based on a complete description of the crystal system and the instrument for data collection is useful. [source]

Is radiation damage dependent on the dose rate used during macromolecular crystallography data collection?

Hanna-Kirsti S. Leiros
This paper focuses on the radiation-damage effects when applying the same total X-ray dose to protein crystals at different dose rates. These experiments have been performed on both a selenomethionated protein and on bovine trypsin using dose rates that span nearly two orders of magnitude. The results show no clear dose-rate effect on the global indicators of radiation damage, but a small measurable dose-rate effect could be found when studying specific radiation damage. It is hypothesized that this observed dose-rate effect relates to differences in the steady-state free-radical concentration. [source]

X-ray-induced debromination of nucleic acids at the Br,K absorption edge and implications for MAD phasing

E. Ennifar
Multi-wavelength anomalous dispersion (MAD) using brominated derivatives is considered a common and convenient technique for solving chemically synthesized nucleic acid structures. Here, it is shown that a relatively moderate X-ray dose (of the order of 5 1015,photons,mm,2) can induce sufficient debromination to prevent structure determination. The decrease in bromine occupancy with radiation dose can be accounted for by a simple exponential, with an estimated rate constant at the absorption-peak wavelength, 7.4,(0.8),MGy, that is not significantly different from its value at the absorption-edge wavelength, 9.2,(2.6),MGy (the given e.s.d.s assess the relative closeness of the two values, not their absolute accuracy, which is probably worse). Chemically, these results (and others) are consistent with bromine cleavage resulting from direct photodissociation and/or from the action of free electrons, rather than from the action of hydroxyl radicals originating from water dissociation. The free bromine species (Br,) diffuse too quickly, even in amorphous ice around 100,K, to allow the determination of a diffusion coefficient. From a practical point of view, it is suggested that a single data collection with a crystal consisting of iodinated instead of brominated derivatives could provide both anomalous scattering and SIR phase information by the progressive cleavage of iodine. [source]

Inactivation of Vibrio parahaemolyticus in pure culture, whole live and half shell oysters (Crassostrea virginica) by X-ray

B.S.M. Mahmoud
Abstract Aims:, To study the inactivation effect of different doses of X-ray on Vibrio parahaemolyticus in pure culture, inoculated whole live and half shell oysters and to evaluate the efficacy of X-ray doses on reduction of inherent microflora on oysters. Methods and Results:, X-ray was produced using RS 2400 generator system (Rad Source Technologies Inc.). Pure culture of V. parahaemolyticus, inoculated half and whole shell oysters with V. parahaemolyticus were treated with 00, 01, 05, 075, 10, 15, 20, 30 and 50 kGy X-ray. Surviving bacteria in the pure culture and inoculated oysters, before and after treatment, were enumerated using overlay plating (in TSA then TCBS) and most probable number (MPN) methods. A greater than 60 log reduction of V. parahaemolyticus was observed with 075, 20 and 50 kGy X-ray for pure culture, half shell and whole shell oysters, respectively. Treatment with 075, 20 and 50 kGy X-ray reduced the MPN to <3 for pure culture, half and whole shell oysters, respectively. Treatment with 10 kGy X-ray significantly (P < 005) reduced the inherent micro-organisms on whole shell oysters from 47 01 to less than the detectable limit (<10 log CFU g,1). Conclusions:, X-ray (1,5 kGy) significantly (P < 005) reduced V. parahaemolyticus and inherent microflora on oysters to less than detectable limit (<10 log CFU g,1). Significance and Impact of the Study:, Treatment with X-ray could control pathogenic bacteria and extend the shelf life of oysters. [source]