1,720,956 research outputs found
Synthesis of erythrocyte glutathione in healthy adults consuming the safe amount of dietary protein
No full textBackground: The finding that plasma glutathione turnover decreases as dietary protein intake decreases suggests that the safe amount of dietary protein, although sufficient for maintenance of nitrogen balance, may be insufficient for maintenance of cellular glutathione. Objective: Our objective was to determine the effect of the safe protein intake on the erythrocyte glutathione synthesis rate and its relation with urinary 5-L-oxoproline excretion. Design: Erythrocyte glutathione synthesis and urinary 5-L-oxoproline excretion were measured in young adults (6 men and 6 women) by using an infusion of [13C2]glycine on 3 occasions: initially during the subjects' habitual protein intake (1.13 g · kg–1 · d–1) and on days 3 and 10 of consumption of a diet providing the safe protein intake (0.75 g · kg–1 · d–1). Results: Compared with baseline values, the fractional synthesis rate of erythrocyte glutathione was significantly lower (P < 0.05) on days 3 and 10 of the diet with the safe protein intake. Urinary 5-L-oxoproline excretion increased significantly (P < 0.05) above baseline by the third day of the diet with the safe protein intake and remained elevated. Erythrocyte glutathione concentrations and absolute synthesis rates decreased by day 3 but recovered to baseline values by day 10. Erythrocyte concentrations of cysteine, methionine, and serine remained unchanged, whereas erythrocyte concentrations of glycine, glutamic acid, and glutamine increased significantly by day 10. Conclusion: During adaptation to the safe amount of dietary protein, there are changes in the concentration and kinetics of erythrocyte glutathione that suggest a reduced antioxidant capacity and possible increased susceptibility to oxidant stress
Endogenous glycine and tyrosine production is maintained in adults consuming a marginal-protein diet
No full textBackground: The adequacy of indispensable amino acid supplies has received much attention in studies of protein requirements, but the availability of nitrogen for synthesis and maintenance of the supply of dispensable amino acids has been overlooked.Objective: We aimed to determine whether nitrogen balance and the endogenous supply of the dispensable amino acids glycine and tyrosine can be maintained with a marginal protein intake.Design: Phenylalanine, glycine, and tyrosine kinetics were measured in young adults (6 men, 6 women) on 4 occasions during a reduction in habitual protein intake (1.13 g·kg-1·d-1) to a marginal intake (0.75 g·kg-1·d-1) by using a multiple stable-isotope-infusion protocol.Results: During the 10-d period of marginal protein intake, nitrogen excretion fell initially, then remained constant such that nitrogen balance was negative for the first 2 d and then positive or zero thereafter. Whole-body protein degradation and synthesis predicted from phenylalanine kinetics declined significantly (P < 0.05) over the period of marginal protein intake. Despite the reduction in the amount of glycine and tyrosine derived from whole-body proteolysis, the fluxes of glycine and tyrosine were maintained.Conclusions: The results show that adaptation to a marginal intake of dietary protein consisted of an overall reduction in whole-body protein turnover, net protein catabolism, and the rate of nitrogen excretion. The conserved nitrogen was sufficient to maintain the endogenous synthesis and hence the supply of glycine and tyrosine
Transfer of (15)N from oral lactose-ureide to lysine in normal adults
No full textThe metabolic fate of salvaged urea-nitrogen was explored in normal adults who had consumed a diet that provided 36 g protein/day for 7 days. We hypothesised that the colonic microflora utilise nitrogen derived from urea salvage to synthesise lysine in functionally significant amounts for the host. Oral lactose-[15N15N]ureide is resistant to digestion but is fermented by the colonic microflora to release 15NH3, which can be used for amino acid synthesis. Prime and intermittent oral doses of lactose-[15N15N]ureide were ingested for 18 h, urine was collected every 3 h and stools were collected for a further 2 days. Amino acids were isolated from urine and from faecal bacterial protein and the enrichment measured. Compared with baseline values, there was significant enrichment (atoms per cent excess) in faecal bacterial glycine (0.0526), alanine (0.117), lysine (0.0875) and histidine (0.0487), and in urinary glycine (0.016), alanine (0.0144) and lysine (0.0098), but not hisitidine. These data show that the gastrointestinal bacteria can utilise urea-nitrogen in the formation of essential and non-essential amino acids that are available to the host. We estimate that on this low protein diet the amount of lysine from bacterial synthesis and available to the host may be 30 mg/kg/day. These data have important implications for our current perceptions for the dietary requirements for essential amino acids
Response of hepatic proteins to the lowering of habitual dietary protein to the recommended safe level of intake
No full textThe plasma concentrations of albumin, HDL apolipoprotein A1 (apoA1), retinol-binding protein (RBP), transthyretin (TTR), haptoglobulin, and fibrinogen were measured, and a stable isotope infusion protocol was used to determine the fractional and absolute synthesis rates of RBP, TTR, and fibrinogen in 12 young adults on three occasions during a reduction of their habitual protein intake from 1.13 to 0.75 g·kg–1·day–1 for 10 days. This study was performed to determine whether healthy adults could maintain the rates of synthesis of selected nutrient transport and positive acute-phase proteins when consuming a protein intake of 0.75 g·kg–1·day–1. During the lower protein intake, the plasma concentration of all the proteins, other than HDL-apoA1, remained unchanged. HDL-apoA1 concentration was significantly reduced (P < 0.05) after 3 days of the lower protein intake, but not at 10 days. The rates of synthesis of RBP and TTR declined significantly (P < 0.05), whereas the rate of synthesis of fibrinogen remained unchanged. The results indicate that, when normal adults consume the recommended safe level of protein, 0.75 g·kg–1·day–1, there is a slower rate of turnover of nutrient transport proteins than on their habitual diet. Hence, healthy individuals consuming this amount of protein may be less able to mount an adequate metabolic response to a stressful stimulus
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
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