1,721,105 research outputs found
The interplay of temperature and protons in the modulation of oxygen binding by squid blood
Full text linkAn extensive set of data relating to the binding of oxygen by haemocyanin from the squid Todarodes sagittatus has been collected under various experimental conditions. The results obtained show that, within the range of physiological pH, the concentration of protons affects mainly the high-affinity state of the molecule without significantly affecting the low-affinity state. As far as the effect of temperature is concerned, the data show a characteristic feature which is very similar to that previously described in the case of haemoglobins from Arctic mammals such as reindeer (Rangifer tarandus) and musk ox. (Ovibos moschatus). The shape of the oxygen equilibrium curve shows strong temperature-dependence, since the overall heat of the binding of oxygen to the low-affinity state of the molecule is strongly exothermic and that to the high-affinity state is very close to zero. The results provide an outline of the intramolecular compromise that, through the interplay of temperature and protons, optimizes the loading and unloading of oxygen under the various environmental conditions experienced by this species of squid
Temperature acclimation modulates the oxygen binding properties of the Atlantic cod (Gadus morhua L.) genotypes - HbI*1/1, HbI*1/2, and HbI*2/2.
No full textThe influence of long-term acclimation temperatures in Atlantic cod (Gadus morhua) was studied by growth experiments carried out over a total of 272 individuals. The attention focused on the structural and functional modulation of the five electrophoretically distinguishable genotypes of cod hemoglobin (HbI*1/1, HbI*1/2, HbI*2/2, HbI*1/2b, and HbI*2/2b) and on the correlation with body length/weight. The main results can be summarized as follows. (1) Acclimation to lower (4 and 8 °C) and higher (12 and 15 °C) temperatures favors the expression of, respectively, more anodic and more cathodic hemoglobin components. (2) The optimal O2 transporting features are observed at 12 °C, as well as a saturation-dependent temperature dependence of O2 binding, which furthermore is strongly dependent upon the acclimation background. (3) The optimal growth condition for the three main genotypes (HbI*1/1, HbI*1/2, and HbI*2/2) is associated with T=12 °C. The overall results are consistent with the idea that environmental temperatures constitute a primary factor in the aggregation of individuals physiologically more than genetically homogeneous. This is fully confirmed by careful statistical analysis carried out over a subset of individuals for which the full set of structural (isoelectric focusing), functional (O2 binding), and growth data was available
Subunit-association and functional properties in the hemocyanin of the squid Todarodes sagittatus.
No full textThe association-dissociation behaviour in Todarodes sagittatus hemocyanin has been studied by sedimentation velocity measurements
at different pH values and in the absence and presence of a
number of anions and cations. In the absence of salts the sedimentation
pattern is dominated (about 1002) by a relatively low M.W.
species (20 S), while 10 mM CaCl2 and increasing pH (above 65)
stabilize a larger (30 S) species.
The above data are used as a basic to explain some physiological questions concerning
the nutritional habits of these animals
Oxygen-binding properties of Cephalopod blood with special reference to environmental temperatures and ecological destribution.
No full textThe thermal sensitivity of oxygen binding has been studied at 10, 15, 20 and 25 °C in whole blood from specimens of Neptunea antiqua acclimated to ambient salinities of 24 and 35‰. The O2 affinity is strongly pH-dependent, demonstrating a large reversed Bohr shift below pH8.0. The magnitude of the Bohr shift is not significantly influenced by temperature or ionic concentration. At 35‰, the blood O2-affinity is strongly influenced by temperature (δHapp-≈58.6kJmol−1), while at 24‰ there is almost no temperature sensitivity
Thermodynamics of oxygen binding to arctic hemoglobins. The case of reindeer
No full textThe most surprising characteristic of reindeer hemoglobin (Hb) concerns its response to changes in temperature. Thus, the shape of the oxygen-binding curve is strongly temperature dependent due to the difference in the enthalpy of oxygenation between the T and R state of the molecule. In fact, delta H of oxygen binding to the T state is strongly exothermic whereas that of the R state is very close to zero or possibly positive after correction for the heat of oxygen solubilization. Moreover, the allosteric transition T0----R0 has been found to display a negative delta H and a contemporaneous decrease in entropy, a behavior which is precisely the opposite of what has been reported for other hemoglobins. As a whole, reindeer Hb represents a beautiful example of the significance that comparative studies may have in assessing the general validity of the main properties of the hemoglobin molecule
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Endothermic oxygenation of hemocyanin in the krill Meganyctiphanes norvegica.
No full textThe oxygen affinity of the hemolymph of the krill Meganyctiphanes norvegica, increases with temperature in the pH range 7.4 to 8.1 reflecting an endothermic overall heat of reaction. This striking feature may be of adaptive significance with respect to the feeding excursions of the animal, which at night reaches the warmer phytoplankton-rich surface layers, where the oxygen availability is reduced due to increased temperature and photorespiration
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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