Search results for " Quaternary."
showing 10 items of 146 documents
Oxygen binding and its allosteric control in hemoglobin of the primitive branchiopod crustacean Triops cancriformis
2007
Branchiopod crustaceans are endowed with extracellular, high-molecular-mass hemoglobins (Hbs), the functional and allosteric properties of which have largely remained obscure. The Hb of the phylogenetically ancient Triops cancriformis (Notostraca) revealed moderate oxygen affinity, cooperativity and pH dependence (Bohr effect) coefficients: P50 = 13.3 mmHg, n50 = 2.3, and ϕ = −0.18, at 20 °C and pH 7.44 in Tris buffer. The in vivo hemolymph pH was 7.52. Bivalent cations increased oxygen affinity, Mg2+ exerting a greater effect than Ca2+. Analysis of cooperative oxygen binding in terms of the nested Monod–Wyman–Changeux (MWC) model revealed an allosteric unit of four oxygen-binding sites and…
Keyhole Limpet Hemocyanin Type 2 (KLH2): Detection and Immunolocalization of a Labile Functional Unit h
2000
Keyhole limpet hemocyanin (KLH) is a mixture of two hemocyanin isoforms, termed KLH1 and KLH2. Within KLH1 eight oxygen-binding functional units (FUs), 1-a to 1-h, have been identified, in contrast to KLH2, which was previously thought to be organized in seven FUs (2-a to 2-g). By limited proteolysis of KLH2 subunits, isolation of the polypeptide fragments, and N-terminal sequencing, we have now identified an eighth FU of type h, with a molecular mass of 43 kDa. This is unusually small for a FU h from a gastropodan hemocyanin. It is also shown that KLH2 didecamers can be split into a stable and homogeneous population of decamers by dialysis against 50 mM Tris/HCl, pH 7.5, in the absence of …
Early stages of beta2-microglobulin aggregation and the inhibiting action of alphaB-crystallin
2008
The interest of nucleation of protein crystals and aggregates (including oligomerization) spans from basic physics theory all the way to biophysics, nanophysics, clinical sciences, biotechnologies, food technologies and polymer-solvent interactions. Understanding nucleation within a theoretical framework capable of providing quantitative predictions and control of nucleation rates, or even the very occurrence of crystallization, is a long-sought goal of remarkable relevance to each of the above fields. A large amount of work has been aimed at such goal, but success has been so far rather limited. Work at our laboratory has more recently highlighted a direct link between nucleation rates and…
YTTRIUM AND REE SIGNATURE RECOGNIZED IN CENTRAL MEDITERRANEAN SEA (ODP SITE 963) DURING THE MIS 6 – MIS 5 TRANSITION
2010
The Mediterranean Sea acts as a miniature ocean with the development of its own conveyor belt. It constitutes an ideal location to study and forecast how the marine environment responds to rapid climatic change. Here we present a palaeoenvironmental study carried out on the sediments of ODP Site 963, recovered in the Sicily Channel, the sill which divides the western from the eastern Mediterranean basin. We focused on the transition between the penultimate glacial (MIS 6) and the last interglacial (MIS 5), between approximately 130 and 115 kyr BP. A novel approach is proposed, taking into account centennial-scale geochemical data on major elements, selected trace elements, and yttrium and R…
Le Quaternaire franc-comtois. Essai chronologique et paléoclimatique.
1982
Le but de ce travail est d'établir le cadre chronologique et paléoclimatique du Quaternaire en Franche-Comté à partir de l'étude des formations édifiées au cours de cette période.Deux grands types de dépôts ont été plus particulièrement étudiés: ·- Les remplissages karstiques d'avens, de porches de grottes et d'abris sous roche, donnant un éclairage intense, mais ponctuel, de l'environnement physique et biologique, grâce aux faunes abondantes et aux indices climatiques d'ordre sédimentologique.- Les dépôts glaciaires et paraglaciaires (moraines, fluvioglaciaires, glacio-lacustres) qui permettent de situer des coupures climatiques au cours du temps dans l'espace géographique étudié.L'étude d…
Phylogeographical footprints of the Strait of Gibraltar and Quaternary climatic fluctuations in the western Mediterranean: a case study with the grea…
2005
Correspondance: cosson@supagro.inra.fr; International audience; We used mitochondrial cyt b sequences to investigate the phylogenetic relationships of Crocidura russula (sensu lato) populations across the Strait of Gibraltar, western Europe, Maghreb, and the Mediterranean and Atlantic islands. This revealed very low genetic divergence between European and Moroccan populations. The application of a molecular clock previously calibrated for shrews suggested that the separation of European from Moroccan lineages occurred less than 60 000 bp, which is at least 5 million years (Myr) after the reopening of the Strait of Gibraltar. This means that an overwater dispersal event was responsible for t…
Transmission Electron Microscopy of GroEL, GroES, and the Symmetrical GroEL/ES Complex
1994
Two new 2-D crystal forms of the Escherichia coli chaperone GroEL (cpn60) 2 x 7-mer have been produced using the negative staining-carbon film (NS-CF) technique. These 2-D crystals, which contain the cylindrical GroEL in side-on and end-on orientations, both possess p21 symmetry, with two molecules in the respective unit cells. The crystallographically averaged images correlate well with those obtained by other authors from single particle analysis of GroEL and our own previous crystallographic analysis. 2-D crystallization of the smaller chaperone GroES (cpn10) 7-mer has also been achieved using the NS-CF technique. Crystallographically averaged images of GroES single particle images indic…
Probable root structures and associated trace fossils from the Lower Pleistocene calcarenites of favignana island, southern italy: dilemmas of interp…
2012
Two types of large, branched structures from the Lower Pleistocene (Calabrian) high-energy calcarenites of Favignana Island are described: Faviradixus robustus gen. et sp. nov. and Egadiradixus rectibrachiatus gen. et sp. nov. They may be interpreted as root structures of large plants, trees and trees or shrubs, respectively. The former taxon co-occurs with the marine animal trace fossils Ophiomorpha nodosa , Ophiomorpha isp., Thalassinoides isp. and Beaconites isp. The interpretation as root structures although tentative is probable and can be related to short emergence episodes for the formation of E . rectibrachiatus or to longer emergence, responsible for the discontinuity at the base o…
Molecular Structure of the Arthropod Hemocyanins
1992
Hemocyanin is an extracellular, blue protein that occurs in high concentrations in the blood of many arthropods, including spiders, scorpions, horseshoe crabs, crustaceans, and at least two centipedes. Serving as an ### oxygen carrier, it is functionally equivalent to hemoglobin, but performs reversible oxygen binding between two copper ions. Hemocyanin is composed of a number of subunits that assemble in an extremely large macro-molecular entity. These particles, which are similar in size to viruses or ribosomes, exhibit a complex allosteric behavior during oxygen binding. There is growing evidence that this functional plasticity has evolved upon, and answers to, ecophysiological constrain…
Polymer-coated reversed-phase packings with controlled hydrophobic properties
1992
Abstract We have designed and synthesized novel reversed-phase packings of non-porous and porous polymethacrylate-coated silicas. By varying the hydrophobicity of the polymer coating, selective unfolding of polypeptides may be achieved, thus enabling manipulation of the chromatographic profile. This study characterizes these packings through their employment for separations of model synthetic peptides of defined secondary, tertiary and quaternary structure. Thus, the packings were applied to the reversed-phase separation α-helical amphipathic and non-amphipathic peptides of the same amino acid composition but different sequences. In addition, selective unfolding of model to-stranded α-helic…