Showing papers by "University of Seville published in 1983"

Selection of wine yeasts for growth and fermentation in the presence of ethanol and sucrose.

Abstract: To optimize the conversion of carbohydrates to ethanol, strains of several Saccharomyces species were examined for the ability to grow and ferment in a range of sucrose and ethanol concentrations. A total of 632 wine yeasts, most of them isolated from wineries in Andalusia and Extremadura, southwestern Spain, were subjected to screening and selection. Growth and fermentative capacity in different ethanol and sucrose concentrations varied from one strain to another. There was no correlation between growth and fermentative capacity. The best 35 strains grew in 15% ethanol and fermented in 18% ethanol. Ethanol accumulated, although at a reduced rate, after the cells stopped growing. Most yeast strains were highly fermentative in 50% sucrose. Some of them effectively utilized the carbohydrates of the culture, yielding final ethanol concentrations of > 14%. Of the 35 selected strains, 16 were promising for genetic analysis and breeding because of their capacity to sporulate. These strains were homothallic, and their spores were viable. The meiotic products analyzed so far were also homothallic.

Utilization of nitrate, nitrite and ammonium by Chlamydomonas reinhardii : Photoproduction of ammonium.

Abstract: In phototrophically grown Chlamydomonas cells, ammonium strongly inhibited the utilization of nitrate or nitrite. Under darkness, or in the presence of an uncoupler or inhibitor of the non-cyclic photosynthetic electron flow, the utilization of nitrate, nitrite or ammonium was suppressed. l-Methionine-d,l-sulfoximine (MSX) or azaserine, which blocks the assimilation of ammonium, inhibited the consumption of nitrate, but not nitrite, by the cells. Ammonium produced an immediate inhibition of the permease for nitrate in Chlamydomonas growing with nitrate, while ammonium-grown cells lacked this permease. The synthesis of nitrate-reductase activity was dependent on an active permease. In N-starved Chlamydomonas cells, previously treated with MSX, the permease for nitrate was insensitive to inhibition by ammonium, and a significant amount of nitrate reductase was synthetized. These cells photoproduce ammonium by reducing nitrate. Nitrogen-repleted cells, treated with MSX, actively photoproduced ammonium by reducing nitrite, but not nitrate.

Separation, Purification, and Characterization of Two Isoforms of Glutamine Synthetase from Chlamydomonas reinhardii

Abstract: Two isoforms of glutamine synthetase. GS1 and GS2, have been separated from Chlamydomonas reinhardii cells grown autotrophically with nitrate. The intracellular level of GS2 was higher than that of GS1. In cells under darkness, the GS1 peak increased markedly, whereas that of GS2 became negligible. The two isoenzymes were purified to electrophoretic homogeneity by a method which included: a) DE-52 cellulose chromatography; b) ammonium sulphate fractionation: and c) affinity chromatography on ADP-sepharose. The specific activity was 114 and 63 U/mg for GS1 and GS2 respectively, and both enzymes (Mr = 380 000 and 373 000) are oligomeric proteins composed by 8 subunits of similar size (Mr = 48 000 in GS1, and 46 000 in GS2). The basic differences between GS1 and GS2 are: a) the effect of light on their intracellular level: b) their Km for ammonium (83 and 244 μᴍ, respectively). Both isoenzymes were inhibited in a similar extent by ʟ-alanine, ʟ-glycine and ʟ-arginine.

Structure of Cyst Wall Precursors and Kinetics of Their Appearance During the Encystment of Laurentiella acuminata (Hypotrichida, Oxytrichidae)1

Abstract: The encystment of Laurenliella acuminata was divided into five stages: stage A (precystic semitransparent cell with dark-globules), stage B (precystic transparent cell), stage C (precystic pigmented cell), stage D (spherical shape without cyst wall) and stage E (young resting cyst), on the basis of observations of changes in morphology and pigmentation during encystment The duration of these stages was also established Observations by electron microscopy confirmed that the cyst wall, composed of four layers, is derived from different kinds of precursors which are synthesized “de novo” The ectocyst precursors are composed of stacks of between 5 and 12 small thin plates or discs; these stacks are about 09 μm in length and 006 μm in height The mesocyst precursors are fibrillar bodies of variable shapes, about 24 μm in maximum length and 012–016 μm in diameter These precursors appear in the cytoplasm of the precystic cell during the first precystic stage (stage A) The endocyst precursors are rounded bodies surrounded by a fine membrane, and their contents appeared similar to the endocyst The granular layer precursors are spherical bodies about 01–02 μm in diameter, surrounded by a double membrane presenting ribosomes adhering to its outer membrane Both endocyst and granular layer precursors are observed in the precystic cytoplasm from stage B On the basis of ultrastructural studies, a formation and growth model of the cyst wall of the hypotrichous ciliate Laurentiella acuminata is proposed

Stereochemistry of organic sulphur compounds: 12—Configurational assignment of 2-methylsulphinyl-1-phenylethanol and some O-derivatives

Abstract: The conformational analysis of the diastereomeric 2-methylsulphinyl-1-phenylethanol and its O-methyl and O-acetyl derivatives has been performed by 1H NMR spectroscopy. The study of the influence of dilution and solvent polarity changes on the coupling constants has permitted the configurational assignment of each diastereoisomer. The role played by hydrogen bonding in the hydroxysulphoxides has also been studied by IR spectroscopy.

Activation of rare earth oxide catalysts

Abstract: It has previously been shown that even the heaviest rare earth oxides undergo partial conversion to bulk hydroxycarbonates when exposed to air. However, when rare earth oxides are used as catalysts, activation temperatures lower than those necessary to achieve the complete removal of H 2 O and CO 2 are often reported. To elucidate the actual active phases that operate in catalytic processes involving rare earth oxides, a systematic temperature-programmed desorption study of La 2 O 3 , Sm 2 O 3 and Yb 2 O 3 was carried out. Our results lend support to a particle structure for the activated powder “oxides” consisting of an oxycarbonate nucleus surrounded by an outer oxide layer.

Morphogenetic Pattern in Laurentiella acuminata (Ciliophora, Hypotrichida): Its Significance for the Comprehension of Ontogeny and Phylogeny of Hypotrichous Ciliates1

Abstract: Morphogenetic events during division, physiological reorganization, and postraumatical regeneration, the last being induced both chemically and microsurgically, were studied by light microscopy on protargol-impregnated specimens of the hypotrichous ciliate, Laurentiella acuminata. Parakinetal stomatogenesis, from transverse cirrus-1 during division and reorganization, changes during regeneration to a parakinetal one which characterizes more primitive members of Hypotrichida in the S. O. Stichotrichina, but solely when the AZM is damaged. These morphogenetic events a) confirm the previous inclusion of L. acuminata among the Oxytrichidae on the basis of its morphological characters and indicate that it is a primitive species of this family related with the Stichotrichina through genera Pleurotricha and Paraurostyla; b) suggest a synthetic model that explains both the positioning and timing of cortical morphogenesis in the cell cycle. The key point of this model is the attribution to the AZM of a repressive capacity on the stomatogenic area, the last one being positioned according to the system of gradients of morphogenetic activity proposed by Jerka-Dziadosz to explain location of primordia in urostylids. This repression is manifested not as a gradient, as indicated by De Terra, but as a long-term repression limited to a certain distance. Simultaneous repression and stimulation occurring in a growing cortex with the AZM remaining constant in size could explain the critical ratio, buccal cortex/somatic cortex, at which stomatogenesis is triggered as indicated by De Terra.

Early development of the granule cell in the cerebellum of the chick embryo

Abstract: The sequence of differentiation of the cerebellar granule cell in chick embryos from the eighth to the 15th days of incubation has been studied in Golgi-stained celloidin sections. In the germinal-cell phase, the presumptive granule cell sends out one or two horizontal processes which may originate either in the body of the cell or in the extension which attaches it to the pial surface. Thus the germinal cell may be converted into either a monopolar or a bipolar presumptive granular cell. Bipolar cells may have two processes of the same length (symmetrical cells) or of unequal length (asymmetrical cells). In the symmetrical as well as asymmetrical bipolar cells the leading process is formed, by means of which the perikaryon emigrates until it situates itself definitely in the internal granular layer. Thus, symmetrical and asymmetrical bipolar cells give rise to a granule cell with parallel fibers of equal or different lengths. The monopolar element may originate a second process or may remain in the monopolar phase until it reaches the internal granular layer. Once there, it completes the formation of the parallel fibers.

Water chain intervention in hydrolytic and tautomeric reactions

Abstract: Water chain intervention in the hydrolysis of methyl fluoride and in some tautomeric 1,3 proton transfer reactions has been studied. The results show that in solution the process are neither unimolecular nor bimolecular as in the gas phase, but are multimolecular, where the geometric parameters of the solvent intervene in the reaction coordinate.

Induction by N-methyl-N′-nitro-N-nitrosoguanidine of nuclear and cytoplasmic mutations in Saccharomyces cerevisiae

Abstract: Mutant frequencies following exposure of Saccharomyces cerevisiae to N -methyl- N ′-nitro- N -nitrosoguanidine (henceforth, MNNG) depend to a great extent on the survival level, and only slightly on the particular experimental conditions under which that survival level was obtained. Nuclear mutations were monitored by studying those conferring resistance to L -canavanine. Their frequency among the survivors reaches a maximum with treatments that leave about 20% of the cells alive and decreases with heavier treatments. The maximal mutagenicity is conveniently achieved by exposing a suspension of about 10 8 early stationary-phase cells to 20 μg MNNG in 1 ml Tris-maleate buffer (0.05 M, pH 7.8) for 10 min at 37°C, with occasional shaking to prevent sedimentation. Even higher frequencies of canavanine-resistant mutants can be obtained by culturing the treated cells in nutrient broth for about 8 h prior to plating in selective medium. Petite mutants induced by MNNG were found to be cytoplasmic. Their frequency increases continuously with dose until they make up virtually the whole surviving population. Yeast and bacteria differ with respect to the dependence of MNNG mutagenesis on pH and physiological state of the cells. They also differ with respect to the relationship between mutagenesis and survival. As an application of MNNG mutagenesis, we have isolated thermosensitive auxotropic mutants from S. cerevisiae and Escherichia coli . From a study of the mutants, the genome of S. cerevisiae is estimated to contain about 3 times as many genes as that of E. coli . Since this roughly corresponds to their respective DNA contents, both genomes must be populated with genes to about the same density.

Point defect and diffusion properties in oxides from high temperature creep

Abstract: A study of high temperature creep properties of non-stoichiometric CU2O, CoO and NiO has been performed at various temperatures and oxygen activities (Po 2). Creep rates are directly related to point defects responsible for the diffusion of the slowest species. These point defects have been tentatively identified by the Po2 dependence of creep rate which does not depend on the detailed mechanism of deformation.

Light as an energy source in continuous cultures of bacteriorhodopsin-containing halobacteria.

Abstract: The role of light as an energy source for slightly aereated cultures of halobacteria was studied, using continuous cultures with low nutrient concentrations and a low oxygen supply. A series of experiments were carried out with non-illuminated and differently illuminated cultures and with different oxygen transfer rates. Under low oxygen availability, light proved to be a decisively important energy source that allowed the populations to reach higher growth rates and much higher population densities. Oxygen influenced the growth over only a minimal level, below which neither the illuminated nor the dark cultures were affected by the oxygen transfer rate. From these results, it appears that the bacteriorhodopsin-mediated energy supply could have a very important role for the ecology of halobacteria in their microaerophilic habitats. In the illuminated cultures, cells that originated purple colonies on plates appeared. These cells, which could be bacteriorhodopsin-constitutive mutants, are now being studied.

Critical examination of the DTA techniques used to study the kinetics of solid-state transformations

Abstract: The use of the different equations proposed to study the kinetics of the glass-to-crystal transition from DTA curves has been extended to include the evaluation of the kinetic parameters of polymorphic transitionS. The transformation kinetics of CaCO3 (aragonite to calcite) and PbO (litharge to massicot) are the examples studied. The kinetic results of both transformations, obtained by the analysis of DTA curves, differ widely from those revealed by the analysis of the isothermal kinetic data. This discrepancy is probably due to erroneous simplifications used in deriving the equations applied in non-isothermal conditions.

Reversible Adsorption of H2 on Rh/TiO2

Abstract: Volumetric adsorption, ESR, NMR and IR measurements have been used to study the effect of H 2 adsorption and desorption at 295 K on a TiO 2 -supported rhodium catalyst. Three situations have been differentiated along the reduction process of the samples from RhCl 3 /anatase to Rh (metal)/rutile: (a) when rhodium is stabilised as Rh + a small part of the important H 2 adsorption is in close interaction with the support; (b) in the situation Rh°/anatase a more substantial amount of the adsorbed hydrogen is spilt reversibly over the support; (c) H 2 adsorption is small after reduction and pumping at 773 K, but a certain amount of hydrogen has been stabilised inside the rutilised support during the high-temperature treatment.

Comparative Concentrations of Cefoxitin in Human Lungs and Sera

Abstract: Eleven patients about to undergo pulmonary surgery received a bolus injection of 1 g of cefoxitin The concentrations of cefoxitin in the serum 1 and 2 h after dosage were 385 ± 189 and 237 ± 256 μg/ml; the lung concentrations at the respective times were 126 ± 07 and 1006 ± 043 μg/ml

When is Lp(μ) Contained in Lq(μ)

Abstract: (1983). When is Lp(μ) Contained in Lq(μ)? The American Mathematical Monthly: Vol. 90, No. 3, pp. 203-206.

Nitrate Reductase from a Mutant Strain of Chlamydomonas reinhardii Incapable of Nitrate Assimilation

Abstract: Nitrate reductase from mutant 305 of Chlamydomonas reinhardii has been purified about 90-fold and biochemically characterized. The enzyme can use reduced flavins and viologens as electron donors to reduce nitrate but, unlike the nitrate reductase complex from its parental wild strain, lacks NAD(P)H-nitrate reductase and NAD(P)H-cytochrome c reductase activities, does not bind to Blue-Agarose or Blue-Sepharose and exhibits a significantly lower molecular weight (177.000 vs. 241.000), whereas its kinetic characteristics and its sensitivity against several inhibitors and treatments are very similar to those of the terminal nitrate reductase activity of the wild strain complex. Spectral studies and antagonistic experiments with tungstate show the presence of cytochrome b557 and molybdenum. These facts lead us to propose that nitrate reductase from mutant 305 has a protein deletion which affects the pyridine nucleotide binding region of the diaphorase protein but without any effect on the terminal nitrate reductase activity.

Salt effects in the reaction of hexacyanoferrate(II) with periodate

Abstract: The effects of various salts on the kinetics of ferrocyanide oxidation by periodate are reported. The reaction exhibits salt effects of low specificity at low concentrations of the added salts ( K+>Na+ and tetralkylammonium ions have a comparable (Et4N+) or even greater (Me4N+) accelerating effects than alkaline cations.

The Interplexiform Cell in the Chameleon Retina

Abstract: A microscopic study of the retina of the adult chameleon has been carried out, following the Golgi staining method as modified by Colonnier.As a result of the observations made a cell stock is described, which has been identified on the basis of its characteristics as an Interplexiform Cell, and two different types of this cell are described.