1,721,211 research outputs found
Oxalate, glycolate, glycerate, sulfate, and citrate
No full textMeasurement of oxalate in urine is important for diagnosis of primary hyperoxaluria and the secondary forms resulting from excessive intake or abnormal intestinal absorption of oxalate. Determination of glycolic acid is essential for diagnosis of primary hyperoxaluria type I (PH I), caused by low or absent activity of the liver-specific peroxisomal alanine:glyoxylate aminotransferase. Primary hyperoxaluria type II (PH II) is caused by low or absent activity D-glycerate dehydrogenase and hydroxypyruvate reductase activity, leading to elevated urinary excretion of both oxalate and L-glyceric acid. Ion chromatography HPLC is the method of choice the quantification of oxalate, glycolate, and glycerate and use of urinary filter spots is a practical alternative approach for the collection and safe transport of samples to be analyzed for many metabolic disorders
Folates
No full textThis chapter will deal with analytical procedures for 5-methyltetrahydrofolic acid (5MTHF) in cerebrospinalfluid (CSF) and serum. Folic acid is a water-soluble vitamin that functions as a one-carbon donor in various metabolic cycles. It is involved in the biosynthesis of thymidylates and purines, methionine synthesis via homocysteine remethylation, the methylation of phospholipids, the interconversion of serine and glycine, and the metabolism of histidine and formate.It is therefore essential for growth, reproduction, and maintenance of normal body function. The natural form is referred to as folate; it consists mainly of 5MTHF and 10-formyltetrahydrofolate in their polyglutamate derivatives [1]. 5MTHF is the active one-carbon donor. It is transported through the blood–brain barrier to serve for a number of reactions in the centralnervous system.
Serum folate deficiency is known to be associated with megaloblastic anemia, high blood levels of homocysteine, and neural tube defect in newborns as a result of folate shortage of the mother[2, 3]. Cerebral folate deficiency (CFD) is a recently recognized neurological disorder found in several children with psychomotor retardation, spastic paraplegia, cerebellar ataxia, and dyskinesia.These patients have very low 5MTHF in their CSF, normal blood folates [4, 5], and some patients display a high titer of folate receptor-blocking autoantibodies[6].
CFD is further associated with the following inherited metabolic disorders: 5,10-methylen-tetrahydrofolate reductase (MTHFR) deficiency [7], 3-phosphoglycerate dehydrogenase (PGDH) deficiency [8], dihydropteridine reductase (DHPR) deficiency [9], as well as with Rett syndrome [10], and Aicardi-Goutières Syndrome [11]. Furthermore, folate deficiency may be associated with congenital folate malabsorption, severe malnutrition, and formiminotransferase deficiency.
5MTHF was initially measured by microbiological and radioisotope dilution as-say [12, 13], and later by high-pressure liquid chromatography (HPLC) using electrochemical (EC), ultraviolet, or fluorescence detection [14-16]. Compared to other methods, EC detection is more sensitive
Pterins and related enzymes
No full textTetrahydrobiopterin(BH4)cofactor is essential for various enzyme activities, including phenylalanine-4-hydroxylase(PAH), tyrosine-3-hydroxylase(TH), tryptophan-5-hydroxylase(TPH), nitric oxide synthase(NOS), and glyceryl-ether monooxygen-ase(GEMO).The de novo biosynthesis pathway of BH4 from guanosine triphosphate (GTP) involves GTP cyclohydrolase I (GTPCH), 6-pyruvoyl-tetrahydropterin synthase (PTPS), and sepiapterin reductase (SR). Three additional enzymes catalyze the last two steps of reduction: aldose reductase (AR), carbonyl reductase (CR), and 3α-hydroxysteroid dehydrogenase type 2 (HSDH2). Cofactor regeneration requires pterin-4a-carbinolamine dehydratase(PCD)and dihydropteridine reductase (DHPR)[1].
The pteridines, a group to which BH4 also belongs, constitute naturally occurring compounds with a base structure of pyrazino [2,3d] pyrimidine (Fig. 6.1.1). Pteridines with the structure 2-amino-4-oxo are designated by the term “pterins,” and those with the structure 2,4-dioxo by the term“lumazines”(Fig.6.1.1). Two groups of pterins can be distinguished: the first have p-aminobenzoate and glutamate attached to the pterin.These pteridines are designated as conjugated pterins(e.g., folic acid). The second group consists of unconjugated pterins, which contain neither of these two substitutions; instead, substitutions occur at the 6-position of the pterin ring nucleus by the aliphatic side chain.The most important blue-fluorescing unconjugated pterins are neopterin, monapterin, biopterin, isoxanthopterin, primapterin, and pterin(Fig.6.1.1). Several other pterins,like xanthopterin, sepiapterin, and 3’-hydroxy-sepiepterin, are yellow-fluorescing species(Fig.6.1.2). Pterins can exist in different oxidation stages, but only fully reduced forms are biologically active.Biop-terin is present in biologicalsamples as biopterin, 7,8-dihydrobiopterin(BH2), and 5,6,7,8-tetrahydrobiopterin(BH4)(Fig.6.1.3).
In man, BH4 is degraded either nonenzymatically by side-chain cleavage to pterin or is enzymatically metabolized in the gastrointestinal tract to become a lumazine [2]. Pterin and dihydropterin are converted by xanthine dehydrogenase to isoxanthopterin and xanthopterin, respectively[3,4]. It is assumed, however, that most of the ingested BH4 is used as a cofactor(mainly for PAH in the liver)and is catabolized to nonfluorescing compounds;it may even be degraded to CO2 and ammonia
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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