Simultaneous In Situ Quantification of Two Cellular Lipid Pools Using Orthogonal Fluorescent Sensors

Lipids regulate a wide range of biological activities. Since their local concentrations are tightly controlled in a spatiotemporally specific manner, the simultaneous quantification of multiple lipids is essential for elucidation of the complex mechanisms of biological regulation. Here, we report a new method for the simultaneous in situ quantification of two lipid pools in mammalian cells using orthogonal fluorescent sensors. The sensors were prepared by incorporating two environmentally sensitive fluorophores with minimal spectral overlap separately into engineered lipid‐binding proteins. Dual ratiometric analysis of imaging data allowed accurate, spatiotemporally resolved quantification of two different lipids on the same leaflet of the plasma membrane or a single lipid on two opposite leaflets of the plasma membrane of live mammalian cells. This new imaging technology should serve as a powerful tool for systems‐level investigation of lipid‐mediated cell signaling and regulation.     

Peculiar properties of hot plasma formation under the influence of intense femtosecond pulses on the surface of molten metal

The peculiar properties of plasma formation on the surface of different liquid metals by femtosecond laser radiation have been studied. It is shown that plasma formation and generation of hard X-radiation on the surface of molten metal depends substantially on the contrast and weakly on the polarization of laser radiation, which clearly distinguishes the plasma produced in our experiments from the plasma generated on the surface of a solid target.     

Structural investigations of <Emphasis Type="Italic">E. Coli</Emphasis> dihydrolipoamide dehydrogenase in solution: Small-angle X-ray scattering and molecular docking

Dihydrolipoamide dehydrogenase from Escherichia coli (LpD) is a bacterial enzyme that is involved in the central metabolism and shared in common between the pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase complexes. In the crystal structure, E. coli LpD is known to exist as a dimer. The present work is focused on analyzing the solution structure of LpD by small-angle X-ray scattering, molecular docking, and analytical ultracentrifugation. It was shown that in solution LpD exists as an equilibrium mixture of a dimer and a tetramer. The presence of oligomeric forms is determined by the multifunctionality of LpD in the cell, in particular, the required stoichiometry in the complexes.     

Some features of hydrolysis of organic and inorganic substrates by Escherichia coli inorganic pyrophosphatase in the presence of various activator cations

The kinetics of hydrolysis of the inorganic (PP_i) and organic (ATP) substrates by Escherichia coli inorganic pyrophosphatase (PPase) and its mutant forms with Asp42 replaced by Ala, Asn, or Glu was studied. The Mn²⁺ or Zn²⁺ ions were used as activators of the enzymatic reaction. The kinetic parameters of hydrolysis were determined. The inhibitory effect of these cations on substrate hydrolysis was investigated. The dissociation constants were calculated for the Mn²⁺- and Zn²⁺-binding activator and inhibitor subsites of E. coli PPase. The observed hydrolysis rate of PP_i increases in the series Zn²⁺ < Mn²⁺ < Mg²⁺, whereas the potential efficiency of these cations decreases in this series. Hydrolysis of ATP by E. coli PPase occurs only in the presence of Mn²⁺. The reasons for the observed differences in the substrate specificity of the enzyme are discussed.     

Some Possibilities for the Enhancement of Light Sensitivity of Silver Halide Photographic Materials for Holographic Recording by Counter Propagating Continuous- and Pulsed-Radiation Beams

An experimental approach to the development of high-resolution photographic materials for holographic recording by pulsed counterpropagating beams was proposed. The approach features an increase in size of emulsion grains as compared with photographic emulsions for reflection holography using continuous lasers. It was shown that the base industrial process for the fabrication of photographic emulsions designed for recording by copropagating beams might be used to manufacture holographic materials with controllable silver halide grain size and that the holographic sensitivity to both continuous and pulse radiation could be enhanced.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 293–296.Original Russian Text Copyright © 2005 by Ryabova, Vorzobova, Kurilova, Popenko.     

3D Raman bullet formed under filamentation of femtosecond laser pulses in air and nitrogen

Complex experimental study of spectral, spatial and temporal behaviors of the IR shifted component observed under filamentation of the collimated femtosecond laser beam (80 GW, 50 fs, 805 nm) in molecular gases showed that this component behaves like a Raman soliton. Namely, it is confined in all domains: (a) it propagates within the filament core, (b) it has a stable duration of 30 fs along the filament, and (c) its spectrum shifts as a whole from 820 to 870 nm on the distance of 2 m from the filament start. A simple model explaining the origin of anomalous group velocity dispersion in the plasma channel of a filament is suggested.     

Investigation of the transformation of the spectrum of femtosecond laser radiation on filamentation in gas medium

The dependence of the parameters of femtosecond laser radiation (55 fs, 3.7 mJ, 800 nm) in a filament on the distance along the filament propagation axis, the diaphragm diameter, and the type and pressure of gas used for filamentation has been studied experimentally.     

Optimization of a femtosecond pulse self-compression region along a filament in air

We have identified the pulse self-compression region in a filament produced by 55 fs, 4 mJ, 805 nm radiation propagating in air without geometrical focusing. In our experiment the pulse self-compression region is attained by the propagation distance, where the shortest wavelength in the supercontinuum blue wing reaches a minimum, and the growing conversion efficiency to white light has a large gradient. Numerical tracking of the pulse along the filament shows a single-peak 9 fs pulse with a flat spectral phase at the optimum compression distance. PACS 42.65.Jx; 42.65.Re; 42.65.Ky