Properties and characterization of soluble forms of lymphocyte acetylcholinesterase from an ox

Two soluble forms of AChE from lymphocyte membrane have been obtained, the Triton solubilized Sd form and the high molar salt solubilized Ss form. They present similar Km (0.10 mM). Hydrodynamic properties of these forms have been studied on saccharose gradients with and without detergent or salt. A similar sedimentation coefficient has been found for these two forms (5.7 S). Lymphocyte plasma membrane AChE is a dimeric form (G2). Without detergent, the Sd form shows multiple secondary forms due to main form polymerization. Increase of NaCl concentration (2M) gives rise to a partial dissociation of these polymers. In the same conditions, the Ss form is not affected. The Ss form centrifugated on cesium chloride gradient has a higher density than the Sd form. These two forms have been treated by HPLC: the Stokes radii are respectively 7.1 nm for the Sd form and 4.5 nm for the Ss form. The molecular weights have been estimated at 175 000 for the Sd form and 105 000 for the Ss form. Pronase enzymatic digestion shows that the Ss form is more rapidly inactivated than the Sd form. Phospholipase C inhibits the Ss form and indicates that this form is a lipid-enzyme complex. The Sd form presents a different behaviour: this form is first activated, and afterwards inhibited by phospholipase C. This behaviour could be due to a more preponderant lipidic environment for the Sd form. The Sd form is probably a detergent-lipid-enzyme complex with an important hydrophobocity. These two forms can be explained by a different association between the enzyme and the phospholipids at the plasma membrane.     

On the insertion of proteins into membranes

Recent data concerning the primary structure and the interactions of proteins with membranes suggest the existence of two classes of integral membrane proteins. In the first class, the polypeptide chain crosses the membrane only once. The membrane penetrating fragment is markedly hydrophobic and contains several positive charges on its C-terminal border. In the second class, the protein is folded in a complex fashion within the membrane and the knowledge of its amino acid sequence is not sufficient to predict the manner in which the protein interacts with the membrane.     

Purification of single-chain human low-molecular-weight kininogen and demonstration of its cleavage by human urinary kallikrein

Human low-molecular-weight kininogen (LMWK) was purified to apparent physical and functional homogeneity by a six-step procedure consisting of ion-exchange chromatography, reverse ammonium sulfate gradient solubilization, hydrophobic chromatography on phenyl-Sepharose, gel filtration, and removal of contaminating proteins by their affinity for Affi-Gel blue and zinc. The recovery averaged 15.6% (n = 4). Purified LMWK presented as a single stained band on alkaline polyacrylamide gel electrophoresis which corresponded to the region of function in eluates from a duplicate gel. The apparent homogeneity was also observed in sodium dodecyl sulfate (SDS)-gel electrophoresis, where the protein presented as a single band of Mr = 65,000 without reduction and 68,000 with reduction. A mole of substrate released 0.8 mol of kinin in 5 min when cleaved by human urinary kallikrein (HUK), and 0.9 mol after 30 min. Cleavage of the single-chain LMWK released kinin from within a disulfide loop as indicated by the SDS-gel electrophoresis of reduced and unreduced kinin-free LMWK. The heavy chain exhibited an Mr = 62,000, which is similar to the Mr of the amino-terminal chain of human HMWK and is consistent with their antigenic relatedness. In contrast to the Mr = 64,000 procoagulant chain of human HMWK, the small (less than 10,000) carboxy-terminal chain of LMWK has no procoagulant activity and may serve only to protect the kinin moiety in the intact substrate.     

Specific perception of ergosterol by plant cells

Ergosterol (a fungal membrane component) induced modification of proton fluxes and membrane hyperpolarization in motor cells of Mimosa pudica. These reactions appear specific since they were not induced by the other sterols tested. A specific desensitization was observed, since cells did not react to a second ergosterol application. Exposed at first to other sterols, cells remained reactive to ergosterol. Comparatively, chitosan (a fungal wall component with known elicitor properties) triggered a membrane depolarization and also induced specific desensitization. This comparative study shows that ergosterol and chitosan are distinctly perceived by plant cells and induced different early events at the plasma membrane level.     

Binding of a tritiated enkephalinergic analog (FK 33-824) to a mitochondrial fraction of rat brain

FK-33-824 (Try-D-Ala-Gly-MePhe-Met(O)ol) is a potent enkephalin analog which has been tritium labelled with a high specific radioactivity (41 Ci/mmole). The labelled drug exhibits specific and saturable binding to rat brain crude mitochondrial fraction. Specific binding is inhibited by low concentrations of morphine, levallorphan and beta-endorphin, suggesting that FK 33-824 [3H] binds preferentially to mu opiate sites. Binding studies at equilibrium and kinetics of formation and dissociation of the labelled ligand-receptor complex indicate that FK 33-824 [3H] binds to two classes of specific sites. Their affinities are distinguishable at 0 degree (KD = 1.3 and 5.8 nM) and very close to each other at 37 degree (KD = 1.9 nM).     

Sunflower seed protein: size and charge heterogeneity in subunits of the globulin fraction

The subunit heterogeneity of the globulin fraction of sunflower seeds was investigated by two dimensional electrophoresis, using isoelectric focusing in the first dimension and sodium dodecyl sulphate polyacrylamide gel electrophoresis in the second dimension. Under non reducing conditions, intermediary subunits B, C and D (molecular weight 54 000, 48 000 and 40 000, respectively) were focused within a pI range 5.4-6.0 but intermediary subunits A (molecular weight 60 000) focused within a pI range 6.3-6.8. Under reducing conditions the electrophoretic patterns show that intermediary subunits consist in large "acidic" and small "basic" subunits linked by disulphide bonds. The large subunits of B species are more acidic and less heterogeneous than the corresponding subunits of the A species. These results confirm that helianthinin had a "legumin-type" structure.     

Ecologie des Dermestidae,une famille de Coléoptères nécrophages associée aux cadavres squelettisés

Lorsqu’un animal meurt, son cadavre forme un écosystème local instable et éphémère où différentes communautés d’insectes nécrophages vont se nourrir. Cette étude a pour but de caractériser les relations entre deux familles fréquentes en contextes médico-légal : les Diptères Calliphoridae et les Coléoptères Dermestidae. Des expériences de choix binaire (olfactomètres en T) et de prédation des Dermestes sur les larves de Diptères ont constitué le 1er axe de notre étude. Il en ressort que l’espèce D. maculatus (adultes et larves) n’exerce qu’une très faible prédation sur les larves de L. sericata. En absence de nourriture, les Dermestes sont néanmoins capables de prédater les pupes de L. sericata, et donc de faire disparaitre ces traces particulièrement importantes en entomologie médico-légale et en archéo-entomologie. Le second axe s’est focalisé sur les relations de compétition et d’agrégation entre D. maculatus et D. haemorrhoidalis. Les résultats obtenus n’ont pas mis en évidence de mécanismes de compétition ou d’exclusion entre ces deux espèces pourtant amenées à fréquenter simultanément le même habitat et à exploiter les mêmes ressources. Placées en condition de choix binaire (2 spots identiques), les 2 espèces s’agrègent ensemble. Mais le développement conjoint de ces 2 espèces sur une seule source de nourriture non limitante entraine une baisse significative du taux de survie chez les deux espèces. Au vu de ces résultats, nous avons conclu à la possibilité d’une coexistence de ces différentes espèces (L. sericata, D. maculatus et D. haemorrhoidalis) sur un cadavre.     

How the ear's works work: mechanoelectrical transduction and amplification by hair cells

The sensitivity of our hearing is enhanced by an active process that both amplifies and tunes the movements of the ear's sensory receptors, the hair cells. In a quiet environment, the active process can even evoke spontaneous emission of sounds from an ear. Recent research indicates that, at least in non-mammalian tetrapods, the active process results from the interaction of negative stiffness in the mechanosensitive hair bundles with two motor processes, one due to myosin-based adaptation and the other to Ca2+ -dependent reclosure of transduction channels. These three processes together explain many of the complex phenomena characteristic of the hearing process.     

Status of the so-called African pygmy elephant (Loxodonta pumilio (NOACK 1906)): phylogeny of cytochrome b and mitochondrial control region sequences

Among the African elephants, it has been unanimously acknowledged that the forest elephants (cyclotis form) are peculiar, so that they have been elevated to the specific rank. The development of molecular analyses of extant Loxodonta has only focused on two forms yet: the savannah form (africana) and the forest form (cyclotis), disregarding the so-called pygmy elephants (pumilio or fransseni) the systematic status of which has been debated since their discovery. Therefore, we have sampled nine dwarfed-labelled specimens in collection and eight specimens of typical forest elephants that we compared to three savannah elephants and two Asian elephants. Because of the degraded nature of the nuclear DNA content in bone samples of old specimens, we assayed mitochondrial markers; 1961 bp of the mitochondrial genome were sequenced (over a continuous range spanning the cytochrome b gene, tRNA Thr, tRNA Pro, hypervariable region 1 and central conserved region of the control region). Pumilio and cyclotis are not sister-taxa: the phylogenetic analyses rather account for the inclusion of the so-called pygmy elephants within a monophyletic group of forest elephants sensu lato. The internal structure of this clade reveals to depend on isolation and remoteness between populations, characteristics that may have been extensively influenced by climatic variations during the Quaternary period. We conclude that the specific taxon Loxodonta pumilio (or Loxodonta fransseni) should be abandoned.     

Les brachiopodes carbonifères des Pyrénées centrales françaises: 2: Étude des Orthida et des Spiriferida; biostratigraphie,paléoécologie,paléobiogéographie

This paper follows the first part: Legrand-Blain &alii, 1983,Geobios, n^o 16, fasc. 3.The brachiopods here described from the «Culm are: Schizophoria cf. resupinata, Rhipidomella michelini, Actinoconchus aff. paradoxus, Lamellosathyris gr. lamellosa, Cleiothyridina (Leiothycridina) nov. sp. gr. okensis, Podtsheremia (s.l.) convenarum nov. sp., Neospirifer gr. derjawini, Anthracospirifer (?) sp., Brachythyrina (Anthracothyrina) perextensa nov. subgen., nov. sp., «Spirifer lujkiensis, Zaissania nov. sp., Kitakamithyris or Torynifer (?) sp., Martinia minima. From shales associated with the Ardengost limestones, slightly different faunas are: Podtsheremia (s.l.) convenarum (?), Anthracospirifer (?) sp., Brachythyrina (Anthracothyrina) bressoni nov. subgen., nov. sp., Phricodothyris mosquensis, Martinia buckmani.The brachiopods from Ardengost limestones andassociated shales, well dated, are of upper Serpukhovian age. The «Culm ones might be heterochroneous, with Serpukhovian and (?) Bashkirian elements. The paleoecology of the brachiopods from limestones and associated shales indicates moderate and low energy environments. The «Culm brachiopods display both resedimentation and delicate preservation features. There is evidence of rather close palaeobiogeographic relationships with the northern Sahara: during the late Serpukhovian, a «Sahara-Pyrénées region could be distinguished, at the western part of the vast Tethysian province.