Showing papers by "National University of La Plata published in 1979"

Crystal structure of a eukaryotic initiator tRNA

Abstract: OUR understanding of the molecular structure–function relationship in tRNA rests mainly on three types of information. First, on the common sequence patterns which have emerged from careful examination of many primary structures1–3; second, a wide variety of spectral and other physical and chemical results must be accounted for by the molecular structure4–6; and third, there is the detailed image of the yeast tRNAPhe molecule independently determined and refined from two different—albeit similar—crystal forms7–10. It is also clear, however, that the molecular model deduced from the yeast tRNAphe crystal structure cannot be easily reconciled with all structural requirements for function and is best considered a well-defined and stable canonical form of tRNA which is packed in an unusually well-ordered way in specific crystal lattices. Notwithstanding the enormous value of this canonical form in explaining the basic architectural features of tRNA, it is clearly important to image other crystalline tRNAs; particularly tRNAs that exhibit different functions (such as, initiators) or have significantly different covalent structures (for example, class III tRNAs)1 or those that crystallise in different solvent conditions. We report here the initial results of the crystal structure determination of a eukaryotic initiator tRNA crystallised from a highly polar aqueous solvent11,12. Its architecture is essentially the same as crystalline yeast tRNAphe, except for a small but significant difference in the position of the anticodon arm.

Prenatal protein depletion and Δ9, Δ6 and Δ5 desaturases in the rat.

Abstract: Pregnant rats were kept throughout gestation on a control diet (i.e., 25% protein), on a low protein diet (i.e., 5% protein) or on a fat-free diet. At 20-21 days of gestation, the rate of 9-, 6-, and 5-desaturation was measured, using microsomes from maternal and fetal livers and placenta microsomes. The effect of protein malnutrition was more evident upon Δ6-desaturase activity from maternal liver, while a less severe reduction in the activities of Δ9- and Δ5-desaturases was observed. No measurable activities of Δ5- and Δ6-desaturases were observed in fetal liver and placenta, while a low activity of Δ9-desaturase was detected in both tissues from the three groups under study. We concluded that Δ6-desaturation is greatly affected by maternal protein deprivation, and this fact could affect the normal supply of polyunsaturated fatty acids for the normal fetus growth and tissue development.

Fatty acid metabolism in the calanoid copepodParacalanus parvus: 1. Polyunsaturated fatty acids

Abstract: The metabolic fate of radioactive linoleate and α-linolenate administered to the South Atlantic copepodParacalanus parvus was studied. The wild copepod was able to incorporate the labeled acids dissolved in seawater. The radioactive linoleate was elongated to 20∶2ω6 and 22∶2ω6 and desaturated by a Δ6 desaturase to 18∶3ω6. α-Linolenate was also desaturated by a Δ6 desaturase to 18∶4ω3 and elongated to 20∶3ω3. The copepod was able to convert α-18∶3 to 20∶5ω3 and 22∶6ω3.

Lipid binding properties of a factor necessary for linoleic acid desaturation

Abstract: Suspension and centrifugation of crude microsomes of rat liver in low ionic strength solution separated a soluble protein fraction that is necessary for the full activity of the linoleic acid desaturase. The fraction partially purified through Sephadex G-150 still retains lipids which are mainly constituted by phosphatidylcholine. Linoleic acid predominates in the fatty acid composition. By NaCl gradient centrifugation and electrophoresis in gelatinized cellulose acetate, the factor behaves like a lipoprotein. The factor binds linoleic acid and linolyl-CoA that are desaturated to γ-linolenic acid when incubated with washed microsomes. Albumin does not replace the factor.

Internal mass transfer coefficient within single bubbles. Theory and experiment

Abstract: Mass transfer coefficients inside single rising bubbles are measured in the system SO2, N2—H2O by using a photographic technique. The differential equations which govern the phenomena, including internal toroidal circulation inside the bubble, are also presented. Assumptions are incompressible, steady, irrotational outside flow and inviscid, steady, axisymrnetric inside flow. From the mass transport viewpoint, restrictions are: binary dilute mixture and axial symmetry. The theoretical solution is presented as Sh vs. Pe and a comparison with experiments shows good agreement. Theoretical predictions for a stagnant fluid inside the bubble were also compared with the experimental results. Des coefficients de transfert de matiere dans des bulles isolees ascendantes sont mesures pour le systeme SO2, N2—H2O en utilisant une technique photographique. Les equations differentielles qui decrivent le phenomene sont aussi representees incluant une circulation toroidale interne au sein de la bulle. Les suppositions sont: le flux externe est incompressible, stationnaire, irrotationnel et le flux interne non visqueux, stationnaire, de symetrie axiale. Du point de vue transfert de matiere, les restrictions sont: melange binaire dilue et symetrie axiale. La solution theorique est presentee comme Sh vs. Pe et une comparaison avec les experiences montre une bonne concordance. Les predictions theoriques pour un fluide stagnant au sein de la bulle sont aussi comparees avec les resultats experimentaux.

5s2 5p3 (4S)nl Levels of Xe III

Abstract: Analysis of recent observations of the Xe III spectrum has yielded revised and extended identifications for the 5s25p3(4S)6s, 7s, 6p, 5d, 6d and 4f levels. Four of the previously known twenty-two levels have been rejected whereas sixteen new levels have been added. The ionization energy has been determined from isoelectronic comparisons. The value arrived at, 250 400 ± 300 cm-1, is some 9000 cm-1 lower than the presently accepted value.

Quasi-spin projection in an exactly soluble model

Abstract: An exactly soluble model for the study of projection techniques within the framework of the Hartree-Fock theory is presented. Properties of the exact solutions are analyzed and projections, both before and after variation, are discussed.

On the presence of conspicuous electron dense bodies in the pinealocytes of the pig

Abstract: The pinealocytes of the pig contain a large number of aldehydefuchsin positive granules In order to determine their nature an ultrastructural study was carried out Numerous bodies having a maximal diameter of about 1,600 nm were found These elements showed a great variety of internal structure, ranging from a “homogeneous” content and amorphous dense aggregates to lamellate bodies Although only a few of them displayed a positive reaction for acid phosphatase, their morphological appearance strongly suggests that they belong to the lysosomal system

Das Schwingungsspektrum von Barium-Divanadat

Abstract: The infrared and laser-Raman spectra of crystalline Ba2V2O7 are reported and discussed by means of a “Site Symmetry” analysis.

A xenon ion pumped open dye stream laser

Abstract: A pulsed xenon ion laser with an output power of 1 kW over the blue-green lines was used to pump an open dye stream laser. An efficiency of the order of 40 percent was determined in broad-band mode operation. The bandwidth in this case was 48 nm (from 582 to 630 nm).

Mittlere Schwingungsamplituden und Molekulargeometrie von IOF5

Abstract: Mean amplitudes of vibration for IOF5 have been recalculated from known spectroscopic data using the “Method of the Characteristic Vibrations”. The obtained values are in excellent agreement with those obtained from electron diffraction and microwave measurements and give also a correct picture of the molecular geometry.

Diphosphat als zweizähniger Ligand Spektroskopische Untersuchung des Bis(ethylendia min)‐diphosphatocobaltat(III)‐Anions

Abstract: Das Festkorper-IR-Spektrum von Ba[Co(en)2P2O7]2 · 4 H2O und das Absorptionsspektrum im sichtbaren Spektralbereich einer wasrigen Losung des Komplexes wurden aufgenommen. Die Schwingungs-, Bindungs- und Koordinationseigenschaften der zweizahnigen P2O74− Gruppierung werden kurz besprochen.

Mittlere Schwingungsamplituden der Tetrafluorooxohalat(V)-Anione: ClF4O−, BrF4O− und IF4O−

Abstract: Mean amplitudes of vibration of the title anions have been calculated in the temperature range between 0 and 1,000 K, using recently reported spectroscopic data. The results are briefly discussed and some comparisons with related species are made.

Current state of the investigation of superallowed Fermi β decays

Abstract: Nuclear Structure: Superallowed Fermiβ transitions; derivation of the effective vector (G′v) and induced scalar (f s) coupling constants from experimental data. At the present time, the crucial point in a systematic study of superallowed 0+-0+ β transitions is the evaluation of the isospin impurity correctionδ c. In the literature,δ c is decomposed into two parts,δ c1 and δc2. Several estimates ofδ c1 have been published, while only one is available forδ c2. We analyze the compatibility of the different estimates ofδ c1 with the most recent surveys of experimental data. The simplest evaluation ofδ c1 reported some years ago by Damgaard is found to yield the most satisfactory ℱt values; these provide reliable values of the effective vector coupling constantG v [e.g.,G v=(1.41242+0.00023)×10−49 ergcm3]. These values are in excellent agreement with a recent valueG v=(1.41248+0.00044)×10−49 erg cm3 obtained by Wilkinson on the basis of a phenomenologic approach toδ c. Conversely, the most recent and detailed parentageexpansion approaches toδ c1 lead toℱt values which increase with Z, showing pronounced slopes. This fact might be due to a relative overestimation ofδ c1 for the lighter nuclei. Using the ℱt values calculated withδ c1 as reported by Damgaard, we evaluate the coupling constant for the induced scalar interaction following a procedure described in a previous paper. The mean of such values isf s/f v=(−0.17±0.80)×10−3. In addition, we develop an alternative way of determining a limit forf s/f v using the phenomenological approach toδ c suggested by Wilkinson. This new procedure yieldsf s/f v=(−0.16±0.87)×10−3, a result which is in excellent agreement with that obtained using the former method; both values are consistent with a value of zero, supporting the conserved vector current theory. The better accuracy of the experimental data makes it possible to reduce by a factor of two the limit established in a previous work.

The Infrared Spectra of Some Sulfate-Apatites

Abstract: The infrared spectra of a series of crystalline sulfate-apatites of the type AI 3MII 2(SO4)3X are presented and discussed. It is demonstrated that the sulfate groups are not greatly distorted in these compounds.

Mass spectra of heterocyclic compounds. IV–2,4,5‐Trioxoimidazolidines

Abstract: General fragmentations induced by electron impact of twenty-one examples of 2,4,5-trioxoimidazolidines are rationalized with the aid of metastable transitions, high resolution measurements and deuterium and 18O labelling. The results can be used for the recognition of different types of derivatives.

A mathematical model for the evolution of a host-pathogen system

Abstract: A mathematical model of a particular host-pathogen system has been constructed, considering the expression for the interaction between two and four independent loci in the host and pathogen organisms, assuming a continous generation pattern for its evolution. For this pattern we have found a set of coupled differential equations corresponding to the rate of change in the genetic frequencies of the system. The differential equations have been solved using the Runge-Kutta–Gill numerical method. The solutions are discussed, analyzing the simultaneous attack of one to four virulent races.

Relationship between apparent and true molecular weight in GPC

Abstract: The analytical relationship between the molecular weight averages obtained from an experimental GPC elu tion curve and the true ones is calculated by use of one integration method in order to solve the convolution integral. The knowledge of these relationship signifies an useful tool to carry out critical considerations on the operation of different methods existing for the calculation of the spreading correction and for the elaboration of the calibration function.

Ultrastructural responses of pancreatic β cells to metabolic alkalosis

Abstract: The ultrastructural changes in pancreatic β cells were studied following glucose-induced insulin secretion in vitro, at two different extracellular pH (7.4 and 7.8). The pancreata perfused at pH 7.4 exhibited a biphasic insulin response to glucose challenge together with signs of increased emiocytotic activity and numerous microtubules in the β cells. Conversely, the pancreata perfused at pH 7.8 showed a significant decrease in insulin secretion, and their β cells revealed scarce emiocytotic images and a marked increase of intracellular granulolysis. These results represent the ultrastructural correlate of the reduced insulin secretion produced by metabolic alkalosis in the perfused rat pancreas.