Showing papers by "University of Nice Sophia Antipolis published in 1978"

Induction of the Triglyceride Pathway Enzymes and of Lipolytic Enzymes during Differentiation in a ‘Preadipocyte’ Cell Line

Abstract: The transition of 3T3-L1 fibroblasts to adipocytes is accompanied by a rise in the activity level of the key enzymes of the fatty acid biosynthetic pathway (ATP-citrate lyase and fatty acid synthetase) and also by a more important rise in the activity level of the glycerolphosphate acyltransferase and of the different enzymes of the triglyceride pathway, while the fatty acid uptake by the cells remains at a constant level. This rise is accompanied by a rise in the activity level of the lipolytic enzymes active against triolein among which the lipoprotein-lipase activity. This phenomenon can be prevented by cycloheximide and is not significant when the cells are maintained at the resting state in the absence of insulin. When present both at the growing state and at the resting state, bromodeoxyuridine selectively affects the activity level of the characteristic enzymes of the triglyceride pathway and does not affect the activity level of glucose-6-phosphate and lactate dehydrogenases. A net increase in the triglyceride content of the 3T3-L1 cells is observed during differentiation; it is corroborated by a significant shift towards triglyceride formation when the incorporation of sn[14C]glycerol-3-phosphate into lipids by cell-free homogenate is studied. Our results indicate on the one hand that the level of phosphatidate phosphohydrolase better correlates with the triglyceride content of the cell than any other lipogenic enzyme; they indicate on the other hand that diglyceride:acyl-CoA acyltransferase is a sensitive ‘indicator’ of 3T3-L1 fibroblasts differentiation into adipocytes.

Computation of convolutions and discrete Fourier transforms by polynomial transforms

Abstract: Discrete transforms are introduced and are defined in a ring of polynomials. These polynomial transforms are shown to have the convolution property and can be computed in ordinary arithmetic, without multiplications. Polynomial transforms are particularly well suited for computing discrete two-dimensional convolutions with a minimum number of operations. Efficient algorithms for computing one-dimensional convolutions and Discrete Fourier Transforms are then derived from polynomial transforms.

The 1H Nuclear‐Magnetic‐Resonance Spectra of Neurotoxin I and Cardiotoxin VII4 from Naja mossambica mossambica

Abstract: Two toxins from the venom of Naja mossambica mossambica, neurotoxin I and cardiotoxin VII4, were investigated in aqueous solution by high-resolution 1H nuclear magnetic resonance (NMR) techniques at 360 MHz. The spectral characterization of the proteins included determination of the number of slowly exchanging amide protons which can be observed in 2H2O solution, measurement of the amide proton chemical shifts and exchange rates, characterization of the aromatic spin systems and the internal mobilities of aromatic rings, and studies of the pH dependence of the NMR spectra. For numerous resonances of labile and non-labile protons quite outstanding pH titration shifts were observed. It is suggested that these NMR parameters provide a useful basis for comparative structural studies of different proteins in the large group of homologous snake toxins. As a first application the NMR data presently available in the literature on neurotoxin II from Naja naja oxiana, toxin α from Naja nigricollis and erabutoxin a and b from Laticauda semifasciata have been used to compare these three proteins with neurotoxin I from Naja mossambica mossambica. This preliminary comparative study provides evidence that the same type of spatial structure prevails for these four homologous neurotoxins and that the folding of the backbone corresponds quite closely to that observed in the crystal structure of erabutoxin b. A second application is the comparison of cardiotoxin VII4 from Naja mossambica mossambica with the neurotoxins. The experimental data indicate that the folding of the polypeptide backbone is closely similar, but that the cardiotoxin molecule is markedly more flexible than the neurotoxins.

Traps and emission centres in thermoluminescent ZrO2

Abstract: The thermoluminescence (TL) of heated amorphous ZrO2, doped by Ti, Th, U, Nb, Dy, excited by 253.7 nm or X-radiation is investigated. Six main peaks are observed at 100, 135, 190, 245, 285, and 385 K and their activation energies determined by four methods. It is shown that most traps obey Curie's model, and that the tetragonal form, which coexists with the monoclinic form, is related to the 245 K peak. The analysis of various TL emission spectra indicates that the emission centres are localized and are connected with Ti3+ surrounded by six oxygens. A centre model is discussed in terms of configuration coordinate curves. La thermoluminescence (TL) de la zircone obtenue par cristallisation d'un gel amorphe de ZrO2 et dopee par Ti, Th, U, Nb et Dy, est etudiee apres excitation UV (253,7 nm) ou X. Six pics principaux sont observes a 100, 135, 190, 245, 285 et 385 K, et leur profondeur de piege determinee par quatre methodes. On montre que la plupart des pieges sont bien decrits par le modele hydrogenoide de Curie et que la phase quadratique, qui coexiste en faible proportion avec la phase monoclinique, est liee au pic de TL a 245 K. Les caracteristiques des spectres d'emission de TL et leur evolution en fonction de la temperature suggerent que le centre d'emission est du type localise. Un modele de courbes de configuration est propose en supposant que le centre lu minogene est constitue par Ti3+ entoure de six oxygenes.

The Role of Serum Albumin in the Uptake of Fatty Acids by Cultured Cardiac Cells from Chick Embryo

Abstract: Fatty acids enter the cultured cardiac cells from chick embryo through two mechanisms, one involving a saturable process, the other resembling passive diffusion. Studies of the saturable component, at fixed concentrations of palmitate or of oleate and at increasing concentrations of albumin. show that this protein increases the rate of palmitate uptake with a maximum at palmitate/albumin molar ratios between 7 and 10 while it decreases the rate of oleate uptake under all conditions. Albumin cannot be replaced by other serum proteins; its effect is specific to saturated fatty acids, can be mimicked by the detergent Tween 40 and involves the binding of the fatty acid to the protein. prior to its delivery to the cell. Both with labelled saturated and unsaturated fatty acids the presence of albumin lowers the proportion of unesterified fatty acids and enhances the proportion of esterified fatty acids recovered in the cardiac cell after uptake. A similar effect of albumin was also found with hepatocytes and permanent cell lines. A specific role for serum albumin is presented, which assumes a ‘dispersing’ effect of this protein towards dimers (or higher aggregates) of saturated fatty acids and the entry of fatty acids into the cell as monomers.

Specificity and interactions at the cationic sites of the axonal (Na+, K+)-activated adenosinetriphosphatase.

Abstract: 1 Specificity at the Mg2+ site has been investigated with P-nitrophenylphosphate and dinitrophenylphosphate as substrates. The interaction parameters between the enzyme and its effectors at the Mg2+ site have been determined. Ni2+ and Cd2+ can be added to the series of known Mg2+ analogues. Tb3+ also inhibits the enzymatic activity and appears as a promising tool for further studies since it interacts with the (Na+,K+)-ATPase in a relatively high affinity process. 2 Interactions between the Mg2+ and Na+ sites have been studied by the P-nitrophenylphosphatase activity. Na+ decreases the apparent affinity of the enzyme for Mg2+ without strong modification of the cooperativity index. 3 Kinetic parameters for ATPase, P-nitrophenylphosphatase and dinitrophenylphosphatase activations by K+ analogues have been determined and the pH dependence of the apparent affinity studied. 4 Heterotropic interactions between K+ and Na+ sites have been studied with K+, Tl+ and NH+4. Three substrates have been used. Firstly, with dinitrophenylphosphate, increasing Na+ concentration changes the positive cooperativity for K+ to a negative one, then back to a positive cooperativity. Simultaneously, the apparent affinity increases then decreases. Secondly, with ATP, an increase of the Na+ concentration decreases the apparent affinity for K+ and changes the cooperativity from a negative to a positive one. Thirdly, with P-nitrophenylphosphate, interactions resemble those obtained with dinitrophenylphosphate. When added at concentrations which stimulate the activity, ATP imposes its type of heterotropic interactions between Na+ and K+ sites.

Nucleation of transitions in liquid 3 He- 4 He mixtures

Abstract: We present a complete set of data describing the nucleation both of superfluidity and phase separation at container walls in liquid 3He-4He mixtures. The appearance of superfluidity and the growth of phase-separated films are measured locally at the walls. A theoretical interpretation is given, important results of which are that the phase separation and superfluid transitions become uncoupled when the transitions are localized near the walls and that quantum fluctuations most probably strongly affect the nature of the superfluid nucleation transition at low temperature. Further, comparison of our results with data for transitions in pure 4He films demonstrates that a universality principle governs the transitions in both systems.

Absolute measurement of the 1.06 μm two-photon absorption coefficient in GaAs

Abstract: Comparing the recombination light intensity produced in GaAs by a 1.06 μm pulse inducing two-photon absorption, with the intensity produced by a 0.53 μm pulse, we obtain directly the two-photon absorption cross-section. This method can be generalized to other materials.

Io–U dating of the Ouljian stage from Torre Garcia (southern Spain)

Abstract: IN this note we discuss the reliability of the Io–U dating method and report on the age of fossils from the Ouljian stage, outcropping along the Mediterranean coast in southern Spain. That this method can produce good results is evident from the fact that the measured ages for these fossils, all from the same stratigraphic horizon, show a standard deviation of only 6,100 yr, which is well within our precision limits. The mean age of the samples is 98,000 yr.

Self‐compiling compilers: An appraisal of their implementation and portability

Abstract: Self-compiling compilers are compilers written in the programming language they are made to compile. They constitute a very interesting case of portable programs, and are rapidly gaining in popularity. This paper is an attempt to classify and evaluate the different methods which have been used for writing and transporting such compilers, according to numerous and various criteria. The potential implementor is then given an idea of the important factors to be considered when selecting one of the many implementation methods available. The study is centred around a specific case, the programming language Pascal and its many compilers.

Laser Raman à fibre émettant dans un très large domaine spectral.

Abstract: A very broad stimulated emission of light covering almost the entire visible spectrum is provided by a fused silica fiber Raman laser. The fiber is 3.5–50 m long with a 50-μm diameter, and the exciting light at 5320 A has a power of about 60 kW.

Changes in the atmospheric-lens modulation transfer function used for calibration in solar speckle interferometry

Abstract: A method is described for the calibration of power spectra of nonstellar astronomical objects, by the use of changes in seeing conditions during speckle-interferometric measurements. Results are given for an application of this technique to solar granulation. The correction of 40 analyses, determined with Fried’s parameter r0 ranging between 2.5 and 11.5 cm, provides satisfactory convergence, and thus permits estimation of the solar granulation power spectrum for frequencies up to 2.5 arc sec−1.

On a problem of forced nonlinear oscillations. numerical example of bifurcation into an invariant torus

Abstract: THE PROBLEMS related to nonlinear forced oscillations that engineers are faced with, can generally be reduced to the study of smooth differential systems such as i = X(x, 2, t) depending on a parameter 2, 2x-periodic with respect to time. An extensive literature, theoretical as well as numerical and experimental, deals with the steady state responses of these systems, specially with time periodic solutions. The non uniqueness of these solutions, their change of nature and stability with parameter values are now well known phenomena. The existence, for some values of i, of bounded but not periodic steady state solutions is still being investigated. Such oscillations have experimentally been observed for mechanical systems [I] and for electrical systems [2] and on analog computer models [3]. These oscillations can reach large amplitudes and lead to defective behaviour of the physical system [ 11. So it is of interest to know the domain of initial values and parameter values for which they appear. Let us point out that we are dealing with cases where the system obtained by suppressing the external periodic excitation has no periodic solutions. The work of Moser [4,5] and Cartwright [6] deal with the general theory of these oscillations. A formal approach by the Ritz-Galerkin method can be found in [3,7]. Using a result obtained by Sacker [S] and, in an independent way, by Ruelle and Takens [9] the existence of a torus of solutions is shown for the differential system provided that a specific bifurcating situation happens (see assumptions H,, H,, H, below). The observed oscillations correspond to a solution lying on the torus. Lanford [lo] presents Ruelle and Takens’ results in a form which is, according to us, suitable to study the nonlinear oscillations. In a recent paper [l I] Iooss applies and develops these results for a system of equations of Navier-Stokes type. Then he proves that solutions which bifurcate from the basic time-periodic solution, for some I = i, lie on an invariant torus (the solutions with initials values on the torus lie on the torus) which may be attracting or repelling (for solutions with initial values near the torus). The basic flow looses its stability for 1 = ilc. Following the last author it is possible to carry out numerically the theoretical results as it is shown in Section 4 by an example given by the physic of vibrations. It is not possible to specify the nature of the solutions lying on the torus (quasi periodic? almost

The Ligurian Sea and the Adjacent Areas

Abstract: The Ligurian Sea forms the most northerly element of the western Mediterranean Basin (Fig. 1). More exactly, it appears as the northeastern extension of a vast abyssal depression, sometimes called the Balearic or the Algero–Provencal Basin, and which we propose to call the Algero–Balearic–Provencal Basin. Largely open toward the southwest, the Ligurian Sea is almost everywhere else delimited by continental or island regions: to the northwest, the north, and east by the southeastern coast of France (Provencal coast, Cote d’Azur s.s.) and by the Italian Riviera and Tuscany coast; to the southeast by the islands of the Tuscan Archipelago (principally Elba), which permit open communication by deeps which may exceed 400 m with another Mediterranean basin, the Tyrrhenian Sea. To the south the Ligurian Sea is bounded by the northern and western coasts of Corsica.