1,720,954 research outputs found
THE ISOLATION AND CHARACTERIZATION OF PORCINE ERYTHROCYTE Ca2+ - ADENOCINE TRIPHOSPHATASE
No full textA THESIS IN THE DEPARTMENT OF BIOCHEMISTRY SUBMITTED TO THE COLLEGE OF MEDICINE IN PARTIAL FULFILMENT OF THE DEGREE OF DOCTOR OF PHILOSOPHY OF THE UNIVERSITY OF IBADANThe Ca2+- pumping adenosine triphosphatase, Ca2+-ATPase, (ATP phosphohydrolase, EC 3.6.1.3), was purified from porcine erythrocyte membranes by calmodulin affinity chromatography in the presence of phosphatidylcholine and characterized.
The membrane-bound enzyme in situ has a specific activity of 3.12 ± 0.08 µmoles/mg protein/hour and a Vmax of 3.47 ± 0.21 µmoles/mg protein/hour in the absence of calmodulin. Corresponding values for the purified enzyme are 101.79 ± 5.82 and 112.92 ± 3.87 respectively. Both forms of the enzyme showed biphasic (high and low affinity) Ca2+ activation kinetics, and were stimulated by calmodulin about 7- fold.. Calmodulin increased both the Ca2+ affinity and the Vmax of the enzyme.. The enzyme is also highly sensitive to inhibition by orthovanadate (Ki = 1.6 ± 0.2 µM).
While these properties are consistent with those of the human erythrocyte Ca2+ -ATPase, the specific activity of the enzyme in intact porcine erythrocyte membranes is one order of magnitude higher than in human erythrocytes. The amount of enzyme routinely isolated from porcine erythrocytes is also about 5 times higher than that isolated from human erythrocyte ghosts.
The purified enzyme was reconstituted into asolectin liposomes where it accumulated Ca2+ into the vesicles with a Vmax of 1.43 ± 0.11µmoles Ca2+ per mg. protein per minute. The ATPase activity of the reconstituted enzyme was stimulated 4 - fold by the addition of the Ca2+ - ionophore A 23187. This indicates a tight coupling between ATP hydrolysis and Ca2+ transport.
After electrophoresis 1n sodium dodecyl sulphate (SDS) polyacrylamide gels, the purified enzyme appeared as a single polypeptide with a molecular weight of about 140,000. However, on high resolution gels, two minor bands (2% and 8% of the total proteins respectively) are seen at positions corresponding to 124,000 and 90,000. These are either sub-units or proteolytic degradation products of the intact enzyme. In addition, upon freezing the purified enzyme at -80°C., 1t usually forms aggregates, probably dimers, with a molecular weight of about 250,000 on SDS gels. After incubation with 125I-ca1modulin, all these bands became labeled, suggesting that they are active forms of the purified ATPase.
The enzyme was also subjected to a controlled proteolytic treatment with trypsin and chymotrypsin in the presence of different effectors of its activity. This led to the fragmentation of the ATPase molecule into a number of transient and limit polypeptides. These fragments were separated by electrophoresis on SDS gels and the calmodul1n-blnding polypeptides were detected by the125I-calmodu1in overlay assay. The porcine erythrocyte Ca 2+ - ATPase appears to be more resistant to proteolysis than the human enzyme, as revealed by the time-course of the proteolytic digestion. It also showed slightly different proteolytic patterns from those established for the human erythrocyte Ca2+ -ATPase.
Antibodies were raised in rabbits against the purified porcine erythrocyte Ca2+ -ATPase and used to study immunological cross-reactivity between the human and porcine enzyme. These antibodies cross-reacted with the enzyme from the two species, suggesting that there are immunological, and probably amino acid sequence, similarities between the two proteins.
These findings indicate that (i) the properties of the human and porcine erythrocyte Ca2+ -ATPase are similar, and (ii) porcine erythrocytes might be a good source of the enzyme for molecular studies
Protein Hydrolysates from Cucumeropsis mannii Seed Inhibit Alpha-amylase In-vitro: Potential for Managing Postprandial Hyperglycemia
Full text linkDiabetes mellitus is a significant global cause of mortality. A hallmark of diabetes pathophysiology is postprandial hyperglycaemia (PPH). PPH is defined as a sudden and exponential increase in blood glucose levels after meals, typically above 140 mg/dL, which does not return to pre-meal levels after two to three hours, leading to glucose toxicity, oxidative stress, cardiovascular risks, and diabetes complications. A management option for PPH is the inhibition of carbohydrate-metabolizing enzymes, such as alpha-amylase. However, current inhibitors are associated with gastrointestinal side effects. Therefore, the search for novel inhibitors is a rational research endeavor. Recent studies highlight plant-derived protein hydrolysates as inhibitors of alpha-amylase. In this study, proteins from Cucumeropsis mannii (C. mannii) were isolated using alkaline solubilization-acid precipitation method and enzymatically cleaved using pepsin and pancreatin to yield C. mannii seed protein hydrolysates. The ?-amylase inhibitory property of the hydrolysates was investigated, using starch as the substrate. The IC50 values for ?-amylase inhibition were 8.77 ± 0.35 mg/mL (pancreatin-derived) and 14.80 ± 0.50 mg/mL (pepsin-derived). Kinetic studies indicated uncompetitive inhibition for pancreatin-derived hydrolysate and mixed uncompetitive for pepsin-derived hydrolysate at 9 mg/mL. These results suggest that C. mannii seed protein hydrolysates may aid in postprandial hyperglycemia management through ?-amylase inhibition
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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