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This work deals with the characterization of fragmentation of recycled concrete aggregate (RCA) by the Los Angeles test. The standard testing procedure for the Los Angeles index requires the measurement of the mass passing 1.6 mm after 500 revolutions of the drum. Questions arise on the significance of this measure for RCA as the resistances of the mortar, of the original aggregate and of their interface simultaneously affect the measurement result. In order to clarify the interpretation of such a measure, three aspects were investigated: the influence of the number of revolutions, the evolution of the full particle size distribution and the distribution of mortar in the fractions after the test. The results suggested that the fracture mechanisms are similar between recycled and natural aggregates with some quantitative differences. RCA was less resistant to fragmentation and displayed a non linear evolution of mass passing 1.6 mm with the number of revolutions. During fracture of RCA, mortar progressively accumulates in smaller fractions, with coarse fractions asymptotically behaving like natural aggregates. The analysis of the rate of breakage of the coarsest fraction appeared to be a richer indicator of crushability as a function of time and composition than the amount of the mass passing 1.6 mm: its typical evolution allows estimating a rate of breakage which correlates well with indirect measures of composition (water absorption and density). The possible existence of an asymptote in the rate of breakage of the coarsest fraction suggests that it can be used to estimate at the same time the resistance of the recycled aggregate and of its original natural component, and probably give an estimate of the amount of mortar. [ABSTRACT FROM AUTHOR]

The ability of microbes to metabolize arsenic may have emerged more than 3.4 billion years ago. Some of the modern environments in which prominent arsenic metabolism occurs are anoxic, as were the Precambrian oceans. Early oceans may also have had a relatively high abundance of arsenic. However, it is unclear whether arsenic cycling occurred in ancient environments. Here we assess the chemistry and nature of cell-like globules identified in salt-encrusted portions of 2.72-billion-year-old fossil stromatolites from Western Australia. We use Raman spectroscopy and X-ray fluorescence to show that the globules are composed of organic carbon and arsenic (As). We argue that our data are best explained by the occurrence of a complete arsenic cycle at this site, with As(III) oxidation and As(V) reduction by microbes living in permanently anoxic conditions. We therefore suggest that arsenic cycling could have occurred more widely in marine environments in the several hundred million years before the Earth's atmosphere and shallow oceans were oxygenated. [ABSTRACT FROM AUTHOR]

More than a decade ago, Heliobacteria were recognised to contain a Rieske/cyt b complex in which the cytochrome b subunit is split into two separate proteins, a peculiar feature characteristic of the cyanobacterial and plastidic b6 f complex. The common presence of RCI-type reaction centres further emphasise possible evolutionary links between Heliobacteria, Chlorobiaceae and Cyanobacteria. In this contribution, we further explore the evolutionary relationships among these three phototrophic lineages by both molecular phylogeny and consideration of phylogenetic marker traits of the superfamily of Rieske/cyt b complexes. The combination of these two methods suggests the existence of a “green” clade involving many non-phototrophs in addition to the mentioned RCI-type photosynthetic organisms. Structural and functional idiosyncrasies are (re-)interpreted in the framework of evolutionary biology and more specifically evolutionary bioenergetics. [ABSTRACT FROM AUTHOR]

The effect of para-bromophenacyl bromide (a selective inhibitor of phospholipase A) and pertussis toxin has been investigated on IgE-dependent histamine release and on IgE-dependent macrophage-mediated cytotoxicity. Para-bromophenacyl bromide, inhibited dose-dependently IgE-dependent stimulation of mast cells and macrophages (IC's of 5.0×10 M and 2.5×10 M, respectively). In contrast, pertussis toxin only inhibited the IgE-dependent stimulation of macrophages, whereas the IgE-dependent activation of mast cells was not affected. These results suggest that the transducing mechanisms following the activation of the high affinity receptor for IgE (FcεRI on mast cells) as well as the low affinity receptor for IgE (FcεRII on macrophages) induce the activation of phospholipase A. FcεRII might be coupled to a pertussis toxin sensitive G-protein. [ABSTRACT FROM AUTHOR]

A major gap of knowledge in metalloproteins is the identity of the prefolded state of the protein before cofactor insertion. This holds for molybdoenzymes serving multiple purposes for life, especially in energy harvesting. This large group of prokaryotic enzymes allows for coordination of molybdenum or tungsten cofactors (Mo/W-bisPGD) and Fe/S clusters. Here we report the structural data on a cofactor-less enzyme, the nitrate reductase respiratory complex and characterize the conformational changes accompanying Mo/W-bisPGD and Fe/S cofactors insertion. Identified conformational changes are shown to be essential for recognition of the dedicated chaperone involved in cofactors insertion. A solvent-exposed salt bridge is shown to play a key role in enzyme folding after cofactors insertion. Furthermore, this salt bridge is shown to be strictly conserved within this prokaryotic molybdoenzyme family as deduced from a phylogenetic analysis issued from 3D structure-guided multiple sequence alignment. A biochemical analysis with a distantly-related member of the family, respiratory complex I, confirmed the critical importance of the salt bridge for folding. Overall, our results point to a conserved cofactors insertion mechanism within the Mo/W-bisPGD family. [ABSTRACT FROM AUTHOR]