Showing papers by "University of Córdoba (Spain) published in 1984"
TL;DR: The resistance of nitrogenase towards oxygen inactivation decreased after transfer of autotrophically grown cells into the dark at subsequent stages of increasing culture density and the inactivation was prevented by addition of fructose.
Abstract: Nitrogenase (=acetylene-reducing activity) was followed during photoautotrophic growth of Anabaena variabilis (ATCC 29413). When cell density increased during growth, (1) inhibition of light-dependent activity by DCMU, an inhibitor of photosynthesis, increased, and (2) nitrogenase activity in the dark decreased. Addition of fructose stabilized dark activity and alleviated the DCMU effect in cultures of high cell density.
129 citations
TL;DR: This paper is an attempt at introducing multiple-criteria decision-making techniques to agricultural systems modellers and then demonstrating their use in livestock ration formulation.
74 citations
TL;DR: In this article, the thermal decomposition of NiAl 2 O 4 was studied by X-ray diffraction at temperatures above 600°C and the corresponding spinel was formed by interaction between both oxides at temperatures higher than 1000°C.
42 citations
TL;DR: In this paper, a new exothermal peak, located between the γ-FeOOH dehydration and further transformation to hematite, has been detected in the DSC diagrams.
35 citations
TL;DR: The glutathione reductase from Escherichia coli strain S33 was purified to homogeneity by a simple and fast procedure consisting of two affinity chromatography steps, and the sensitivity towards such mercurial was greatly enhanced after reduction of the enzyme by NADPH.
Abstract: The glutathione reductase from Escherichia coli strain S33 was purified to homogeneity by a simple and fast procedure consisting of two affinity chromatography steps After 40-80% ammonium sulfate fractionation, the enzyme was adsorbed to an N6-2'5'-ADP-Sepharose affinity column from which it was specifically eluted by a 0-10 mM NADP+ linear gradient The enzyme was finally purified to homogeneity after a second affinity chromatography step in a C8-ATPR-Sepharose column, from which it was eluted by means of the same NADP+ gradient Starting from 182 g of E coli cells, 69 mg of pure enzyme was obtained after a 2632-fold purification, with a total yield of 63% The pure enzyme showed a specific activity of 361 U/mg, and its absorption spectrum was characteristic of a flavoprotein, with an A272/A450 of 784 The enzyme was a dimer with a molecular weight 109 000 and 40 A hydrodynamic radius The optimum pH were 75 and 45 with NADPH and NADH, respectively, as reductants Apparent K'm values of 16, 377, and 66 microM were determined at pH 75 for NADPH, NADH, and GSSG, respectively Upon storage the enzyme was stable at pH values ranging from 75 to 95, being additionally stabilized by FAD, NADP+, dithiothreitol, or glycerol The pure enzyme was quite heat stable, denaturing significantly only after 10 min at 70 degrees C A marked activity loss was observed however, even at 0 degrees C, in the presence of 20 microM NADPH The enzyme was inactivated by low concentrations of para-hydroximercuribenzoate; the sensitivity towards such mercurial was greatly enhanced after reduction of the enzyme by NADPH
33 citations
TL;DR: In this article, a general and repetitive method to determine the base strength and number of basic sites of catalysts with low surface area is reported, and the nature of the titrating agent is discussed.
Abstract: A general and repetitive method to determine the base strength and number of basic sites of catalysts with low surface area is reported. The nature of the titrating agent is discussed. The nature of the active sites of a Ba(OH)2 catalyst with low surface area is discussed.
31 citations
TL;DR: Ethanol selection has resulted in a higher ethanol tolerance, a shorter developmental time and a better ability to use ethanol as food, showing the AdhF Adhf genotype to be that with the highest relative fitness.
Abstract: Homozygous AdhF AdhF and Adhs Adhs lines, collected from the same D. melanogaster winery polymorphic population, were submitted to stress by environmental ethanol. The responses of each of the FF, FS and SS genotypes, for both control and selected lines were analysed in normal and ethanol supplemented medium, in relation to three fitness components: egg-to-adult viability, developmental time and ethanol utilisation. Ethanol selection has resulted in a higher ethanol tolerance, a shorter developmental time and a better ability to use ethanol as food, showing the AdhF AdhF genotype to be that with the highest relative fitness.
31 citations
TL;DR: In this paper, the structural properties of the dehydroxylation product, identified as hematite, are determined at different temperatures and a change of crystallite shape has been shown to occur in the range of temperatures of 300 to 485°C.
30 citations
TL;DR: Photometric methods for cyanide determination by normal and reversed FIA techniques and by completely continuous monitoring shows the usefulness of the continuous monitoring method.
29 citations
TL;DR: In this article, several expressions have been developed to differentiate EC and CEC mechanisms when the transfer is reversible, and they have been applied to the pyridine-4-aldehyde reduction and close agreement between the experimental and theoretical results was obtained for a CEC mechanism.
28 citations
TL;DR: In this article, it was shown that ammonium (methylammonium) per se, and not a product of its metabolism, is the co-repressor of nitrate reductase in C. reinhardii.
01 Jan 1984
TL;DR: Examples of adaptive mechanisms and their possible role in yield responses under water stress are presented for sorghum, cotton and sunflower as annuals and orange, almond and olive trees as perennials.
Abstract: SummaryTerrestrial plants have evolved numerous mechanisms which enable them not only to survive, but to achieve substantial productivity levels under drought. Most adaptive mechanisms appear to be directed at either avoiding or tolerating plant water deficits. The sensitivity of leaf area expansion to mild water stress is emphasized, suggesting that it has adaptive significance by acting as a partitioning mechanism which favours root growth and hence improves the shoot water status.Alterations in developmental pathways often aid the plant in avoiding dehydration by adjusting its life cycle to the available water supply. Mechanisms of dehydration tolerance include the control of transpiration and the maintenance of turgor through osmotic adjustment. Examples of adaptive mechanisms and their possible role in yield responses under water stress are presented for sorghum, cotton and sunflower as annuals and orange, almond and olive trees as perennials. There is substantial variability in the degree of express...
TL;DR: In this paper, a configuration for flow injection analysis, which is suitable for simultaneous determinations, is proposed, based on division of the injected sample, with each sub-sample resulting from the division passing through reactors with different characteristics and the confluence of these channels before their arrival at the detector.
TL;DR: The NADH-cyanide-inactivated nitrate reductase remained inactive after removing the excess of NADH and cyanide by filtration through Sephadex G-25, but could be readily reactivated by incubation with ferricyanide or by a short exposure to light in the presence of FAD.
01 Jan 1984
TL;DR: The physiological and enzymatic properties of these L-arabinose non-utilizing mutants suggest that L-Arabinose resistance is due to forward mutations in at least 3 other genes, araA, aRAB and araC, blocking steps prior to L-ribulose 5-phosphate accumulation.
Abstract: The evidence that most animal carcinogens are also mutagens,(20,24) strongly suggesting that DNA is the ultimate target of carcinogenic activation, has been an important support of the somatic mutation theory of the etiology of cancer. The recent demonstration that a single point mutation, a GC to TA transversion, leads to the activation of a human oncogene(30,36) is in agreement with this suggestion.
TL;DR: In this article, the authors proposed some criteria to distinguish between reaction mechanisms from implicit equations found in the bibliography, except for CEC mechanisms (first and second-order post-kinetic) whose equations were obtained from the concept of the reaction layer.
TL;DR: This note sets out to counter the view that goal programming applied to diet planning offers little improvement over conventional linear programming techniques.
Abstract: This note sets out to counter the view that goal programming applied to diet planning offers little improvement over conventional linear programming techniques.
TL;DR: In this paper, a stopped-flow injection method for the determination of copper (II) in the range 0.2 -300 ng ml −1 is proposed, based on the catalytic effect of this ion on the 2,2'-dipyridylketone hydrazone/hydrogen peroxide reaction.
TL;DR: In this paper, the spectrofluorimetric determination of cyanide (0.1 −20 μg ml−1) using a normal flow-injection method and a stopped-flow procedure was reported.
TL;DR: In this paper, a single value of activation energy (193 kJ mol−1) is obtained from the Arrhenius plots, and is relatively independent of the choice of rate law.
Abstract: The kinetics of thermal decomposition of CoOOH have been studied by analysis of isothermal weight loss data under vacuum. The comparison of linear correlation coefficients of different kinetic expressions applied to these data does not allow an understanding of the mechanism, even when significance tests are performed (t test). A single value of the activation energy (193 kJ mol−1) is obtained from the Arrhenius plots, and is relatively independent of the choice of rate law. On the other hand, a change in the mechanism of formation of Co3O4 with temperature cannot be inferred from analysis of isothermal data. Thus, the statement of some authors that from formal kinetics it is possible to distinguish the proton and electron transfers involved in the transformation appears unacceptable.
TL;DR: The amino acid and protein content of mice exposed to enriched, restricted and impoverished environments have been studied in six discrete CNS areas and the results corroborate the proposed plasticity of the aminoacidergic system.
Abstract: The amino acid and protein content of mice exposed to enriched, restricted and impoverished environments have been studied in six discrete CNS areas. Differences between enriched and either restricted or impoverished groups were found whereas no difference was observed between restricted and impoverished ones. In the first case, a significant increase for aspartate was found in spinal cord, whereas glutamate significantly decreased in colliculi and cerebral cortex. Similarly, glycine increased in cerebral cortex and decreased in colliculi and pons-medulla, and γ-aminobutyrate (GABA) increased in spinal cord, pons-medulla and cerebellum and decreased in thalamus-hypothalamus. No changes in concentrations of five non-transmitter amino acids (serine, threonine, alanine, isoleucine, leucine) were observed. Significant increases of the protein concentration in cerebellum and spinal cord were found. The changes were due to enrichment, not to aggregation conditions. The results corroborate the proposed plasticity of the aminoacidergic system.
TL;DR: It is suggested that the results can be explained on the basis of a turnover mechanism involving continued de novo enzyme synthesis and subsequent synthesis of a PAL-inactivating system.
Abstract: Light, excision and sucrose increased extractable phenylalanine ammonia-lyase (PAL) activity from hypocotyl tissue of sunflower (Helianthus annuus L. cv. Peredovik) to 2–6 times the basal level. Intact sunflower seedlings or whole hypocotyls incubated in water or 0.1 M sucrose exhibited, in continuous light, a pattern in which PAL peaked 4 and 28 h after the beginning of the illumination. When 0.5 cm long hypocotyl segments were incubated in water or 0.1 M sucrose, they exhibited, both in continuous light and in the dark, a pattern in which PAL rose during an initial period of 10 h (assay in sucrose and light) to 48 h (assay in water and dark) and then remained nearly constant at a high value for at least the next 10 h. When whole hypocotyls were incubated in 0.1 M sucrose, a third pattern in PAL activity was found in which PAL peaked after 28 h and subsequently declined. In all the above systems the increase in PAL activity was significantly reduced by cycloheximide. Furthermore, the subsequent decay of PAL activity following illumination was prevented by delayed transfer to cycloheximide. It is suggested that the results can be explained on the basis of a turnover mechanism involving continued de novo enzyme synthesis and subsequent synthesis of a PAL-inactivating system.
TL;DR: In this paper, a kinetic method for the determination of nanogram amounts of iron(III) based on its catalysis of the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide in an ammoniacal medium is described.
TL;DR: Polarographic (dc and DP), voltammetric and kinetic studies of the first reduction wave of phenylglyoxal have been carried out in the 0-12 pH range as discussed by the authors.
TL;DR: There is a synthesis of 2,3‐bisphosphoglycerate during the erythropoietic process which parallels the synthesis of haemoglobin in rat bone marrow cells fractionated by density gradient in Percoll.
Abstract: Rat bone marrow cells have been fractionated by density gradient in Percoll. Differential counting of erythroid cells, haemoglobin concentration and bisphosphoglycerate mutase and phosphoglycerate kinase activities have been determined in cellular fractions. As shown by means of a statistical approach, an increase in bisphosphoglycerate mutase activity and a slight decrease in phosphoglycerate kinase activity is found in erythroid cells as their haemoglobin content increases. Our results suggest that there is a synthesis of 2,3-bisphosphoglycerate during the erythropoietic process which parallels the synthesis of haemoglobin.
TL;DR: The results support a tetrameric structure for the C. reinhardii NR complex, containing two kinds of subunits, and the sole activities related to NR present in these mutants responded to tryptic treatment to the same extent as the corresponding activities of the wild enzyme complex.
Abstract: The NAD(P)H-nitrate reductase complex (overall-NR) of Chlamydomonas reinhardii exhibits two partial activities: NAD(P)H-cytochrome c reductase (diaphorase) and reduced benzyl viologen-NR (terminal-NR). Mild tryptic digestion of the enzyme complex resulted in the loss of both overall and terminal-NR activities, whereas diaphorase activity remained unaltered. The diaphorase activity of mutant 104 and the terminal-NR activity of mutant 305 of C. reinhardii, which are the sole activities related to NR present in these mutants, responded to tryptic treatment to the same extent as the corresponding activities of the wild enzyme complex. Trypsin disassembled the 220-kd NR native complex by destroying the aggregation capability of the diaphorase subunits without affecting their activity nor molecular size (45 kd). A 67-kd thermostable protein, containing molybdenum co-factor, was also released from trypsin-treated NR. This protein lacked diaphorase and NR activities but was able to reconstitute the overall-NR complex by complementation with untreated diaphorase subunit of mutant 104. Our results support a tetrameric structure for the C. reinhardii NR complex, containing two kinds of subunits.
TL;DR: In this article, the effects of phenmedipham, propham, carbetamide, lenacil and benzthiazuron on soil nitrification were studied in the laboratory using a perfusion technique.
Abstract: The effects of phenmedipham, propham, carbetamide, lenacil and benzthiazuron on soil nitrification was studied in the laboratory using a perfusion technique. The nitrification process was markedly retarded at a phenmedipham concentration of 50–500μg g−1 soil, so that 55–150 days were required for complete oxidation of supplied NH+4-N as compared with 33 days for the untreated control. Phenmedipham caused a reduction in both the maximum population and the proliferation rate of nitrifying organisms, as evaluated from kinetic parameters. These inhibitory effects showed a low persistance probably due to herbicide breakdown. The effects of 100 μg g−1 soil of propham, carbetamide, lenacil or benzthiazuron on the nitrification process was very weak, although the kinetics of the nitrification process was affected by all these herbicides.
TL;DR: In this article, a kinetic method was presented for the simultaneous determination of iron(III) and manganese(II) based on the different reaction rates resulting from the catalytic effect of both metal ions on the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide in an ammoniacal medium.
TL;DR: The modification to the DeFord and Hume method for differential pulse polarography is applicable to quasi-reversible and irreversible processes and takes into account any change in the reversibility of the system when the concentration of the ligand is altered as discussed by the authors.
TL;DR: In this article, a study of the reduction of pyridoxal 5′-phosphate (PLP) in an acid medium on a d.m.c. and d.p. polarogram was carried out.