Protein Mobility in the Cytoplasm of Escherichia coli

The rate of protein diffusion in bacterial cytoplasm may constrain a variety of cellular functions and limit the rates of many biochemical reactions in vivo. In this paper, we report noninvasive measurements of the apparent diffusion coefficient of green fluorescent protein (GFP) in the cytoplasm of Escherichia coli. These measurements were made in two ways: by photobleaching of GFP fluorescence and by photoactivation of a red-emitting fluorescent state of GFP (M. B. Elowitz, M. G. Surette, P. E. Wolf, J. Stock, and S. Leibler, Curr. Biol. 7:809-812, 1997). The apparent diffusion coefficient, Da, of GFP in E. coli DH5alpha was found to be 7.7 ± 2.5 µm^2/s. A 72-kDa fusion protein composed of GFP and a cytoplasmically localized maltose binding protein domain moves more slowly, with Da of 2.5 ± 0.6 µm^2/s. In addition, GFP mobility can depend strongly on at least two factors: first, Da is reduced to 3.6 ± 0.7 µm^2/s at high levels of GFP expression; second, the addition to GFP of a small tag consisting of six histidine residues reduces Da to 4.0 ± 2.0 µm^2/s. Thus, a single effective cytoplasmic viscosity cannot explain all values of Da reported here. These measurements have implications for the understanding of intracellular biochemical networks

Effect of spray cooling on heat transfer in a two-phase helium flow

International audienceIn this paper, we describe an experimental study of the phenomenon of spray cooling in the case of liquid helium, either normal or superfluid, and its relationship to the heat transfer between an atomized diphasic flow contained in a long pipe, and the pipe walls. This situation is discussed in the context of the cooling of the superconducting magnets of the Large Hadron Collider (LHC). Experiments were conducted in a test loop reproducing the LHC cooling system, in which the vapor velocity and temperature could be varied in a large range. Shear induced atomization results in the generation of a droplet mist which was characterized by optical means. The thin liquid film deposited on the walls by the mist was measured using interdigitated capacitors. The cooling power of the mist was measured using thermal probes, and correlated to the local mist density. Analysis of the results shows that superfluidity has only a limited influence on both the film thickness and the mist cooling power. Using a simple model, we show that the phenomenon of spray cooling accounts for the measured non linearity of the global heat transfer. Finally, we discuss the relevance of our results for cooling the final focus magnets (inner triplets) in an upgraded version of the LHC

Condensation of helium in aerogels and athermal dynamics of the Random Field Ising Model

High resolution measurements reveal that condensation isotherms of $^4$He in a silica aerogel become discontinuous below a critical temperature. We show that this behaviour does not correspond to an equilibrium phase transition modified by the disorder induced by the aerogel structure, but to the disorder-driven critical point predicted for the athermal out-of-equilibrium dynamics of the Random Field Ising Model. Our results evidence the key role of non-equilibrium effects in the phase transitions of disordered systems.Comment: 5 p + suppl. materia

Visualization in cryogenic environment: Application to two-phase studies

11 pagesInternational audienceThis paper reviews recent technical developments devoted to the study of cryogenic two-phase fluids. These techniques span from simple flow visualization to quantitative measurements of light scattering. It is shown that simple flow pattern configurations are obtained using classical optical tools (CCD cam- eras, endoscopes), even in most severe environments (high vacuum, high magnetic field). Quantitative measurements include laser velocimetry, particle sizing, and light scattering analysis. In the case of mag- netically compensated gravity boiling oxygen, optical access is used to control the poistioning of a bubble subject to buoyancy forces in an experimental cell. Flow visualization on a two-phase superfluid helium pipe-flow, performed as a support of LHC cooldown studies, leads to flow pattern characterization. Visu- alization includes stratified and atomized flows. Thanks to the low refractive index contrast between the liquid and its vapor, quantitative results on droplet densities can be obtained even in a multiple scatter- ing regime

A coherent optical link through the turbulent atmosphere

We describe the realization of a 5 km free space coherent optical link through the turbulent atmosphere between a telescope and a ground target. We present the phase noise of the link, limited mainly by atmospheric turbulence and mechanical vibrations of the telescope and the target. We discuss the implications of our results for applications, with particular emphasis on optical Doppler ranging to satellites and long distance frequency transfer.Comment: version 2, modified following comments from colleagues and reviewer

Critical behavior of the liquid gas transition of 4 He confined in a silica aerogel

6 pagesInternational audienceWe have studied 4 He confined in a 95% porosity silica aerogel in the vicinity of the bulk liquid gas critical point. Both thermodynamic measurements and light scattering experiments were performed to probe the effect of a quenched disorder on the liquid gas transition, in relation with the Random Field Ising Model (RFIM). We find that the hysteresis between condensation and evaporation present at lower temperatures disappears at a temperature T ch between 25 and 30 mK below the critical point. Slow relaxations are observed for temperatures slightly below T ch , indicating that some energy barriers, but not all, can be overcome. Above T ch , no density step is observed along the (reversible) isotherms, showing that the critical behavior of the equilibrium phase transition in presence of disorder, if it exists, is shifted to smaller temperatures, where it cannot be observed due to the impossibility to reach equilibrium. Above T ch , light scattering exhibits a weak maximum close to the pressure where the isotherm slope is maximal. This behavior can be accounted for by a simple model incorporating the compression of 4 He close to the silica strands

Recommendations for mechanical ventilation of critically ill children from the Paediatric Mechanical Ventilation Consensus Conference (PEMVECC)

Purpose: Much of the common practice in paediatric mechanical ventilation is based on personal experiences and what paediatric critical care practitioners have adopted from adult and neonatal experience. This presents a barrier to planning and interpretation of clinical trials on the use of specific and targeted interventions. We aim to establish a European consensus guideline on mechanical ventilation of critically children. Methods: The European Society for Paediatric and Neonatal Intensive Care initiated a consensus conference of international European experts in paediatric mechanical ventilation to provide recommendations using the Research and Development/University of California, Los Angeles, appropriateness method. An electronic literature search in PubMed and EMBASE was performed using a combination of medical subject heading terms and text words related to mechanical ventilation and disease-specific terms. Results: The Paediatric Mechanical Ventilation Consensus Conference (PEMVECC) consisted of a panel of 15 experts who developed and voted on 152 recommendations related to the following topics: (1) general recommendations, (2) monitoring, (3) targets of oxygenation and ventilation, (4) supportive measures, (5) weaning and extubation readiness, (6) normal lungs, (7) obstructive diseases, (8) restrictive diseases, (9) mixed diseases, (10) chronically ventilated patients, (11) cardiac patients and (12) lung hypoplasia syndromes. There were 142 (93.4%) recommendations with "strong agreement". The final iteration of the recommendations had none with equipoise or disagreement. Conclusions: These recommendations should help to harmonise the approach to paediatric mechanical ventilation and can be proposed as a standard-of-care applicable in daily clinical practice and clinical research

Rules Governing Selective Protein Carbonylation

BACKGROUND:Carbonyl derivatives are mainly formed by direct metal-catalysed oxidation (MCO) attacks on the amino-acid side chains of proline, arginine, lysine and threonine residues. For reasons unknown, only some proteins are prone to carbonylation. METHODOLOGY/PRINCIPAL FINDINGS:we used mass spectrometry analysis to identify carbonylated sites in: BSA that had undergone in vitro MCO, and 23 carbonylated proteins in Escherichia coli. The presence of a carbonylated site rendered the neighbouring carbonylatable site more prone to carbonylation. Most carbonylated sites were present within hot spots of carbonylation. These observations led us to suggest rules for identifying sites more prone to carbonylation. We used these rules to design an in silico model (available at http://www.lcb.cnrs-mrs.fr/CSPD/), allowing an effective and accurate prediction of sites and of proteins more prone to carbonylation in the E. coli proteome. CONCLUSIONS/SIGNIFICANCE:We observed that proteins evolve to either selectively maintain or lose predicted hot spots of carbonylation depending on their biological function. As our predictive model also allows efficient detection of carbonylated proteins in Bacillus subtilis, we believe that our model may be extended to direct MCO attacks in all organisms