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Harriet Totoe Boakye

Bio: Harriet Totoe Boakye is an academic researcher from University of Massachusetts Amherst. The author has contributed to research in topics: Selenium & Selenium Compound. The author has an hindex of 5, co-authored 5 publications receiving 330 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the complementary role of selenium and sulfur specific chromatographic detection by HPLC with interfaced inductively coupled plasma mass spectrometry (ICP-MS) detection and by derivatization GC with interfacing atomic spectral emission was investigated.

124 citations

Journal ArticleDOI
TL;DR: Gas chromatography with atomic emission detection of ethylated species and fluoroacid ion pair HPLC applied to the analysis of currently produced or archived selenized yeast and Brassica juncea have revealed the presence of a previously unrecognised Se-S amino acid, S-(methylseleno)cysteine.

89 citations

Journal ArticleDOI
TL;DR: The concerted application of element specific atomic spectral detection for chromatographic eluent monitoring allows previously unexploited qualitative and quantitative analytical concepts to be developed for the determination of selenium species as discussed by the authors.
Abstract: The concerted application of element specific atomic spectral detection for chromatographic eluent monitoring allows previously unexploited qualitative and quantitative analytical concepts to be developed for the determination of selenium species. Selenium speciation is vital in order to better understand its metabolism and biological significance in clinical chemistry, biology, toxicology, and nutrition. Fluoroacid ion pair HPLC with ICP-MS detection and GC derivatization with atomic emission detection (AED) together aid analysis and elucidation of reaction pathways of selenium compounds in high selenium enriched yeast, as used widely in nutritional and clinical cancer preventative studies. Comparisons between currently produced and archived selenized yeasts show major differences in speciation. The formation of selenomethionine selenoxide and the identification of Se–S bonded S-(selenomethyl)-cysteine in archived nutritional yeast may be important for short and long term stability and nutritional activity studies.

64 citations

Journal ArticleDOI
TL;DR: Selenium-specific NMR spectroscopic methods were developed to directly analyze the aqueous extracts of the hydrolyzed selenized yeast without derivatization or separation, and Selenomethionine and S-(methylseleno)cysteine were identified by 77Se-1H HMQC-TOCSY experiments.
Abstract: After proteolytic digestion, aqueous extraction, and derivatization with diethyl pyrocarbonate or ethyl chloroformate, HPLC−inductively coupled plasma (ICP)-MS, GC−atomic emission detection (AED), and GC−MS analysis of high-selenium yeast stored at room temperature for more than 10 years showed selenomethionine as the major Se product along with substantial amounts of selenomethionine selenoxide hydrate and the previously unreported selenoamino acid having a Se−S bond, S-(methylseleno)cysteine. The identity of the latter compound was confirmed by synthesis. The natural product was shown to be different from a synthetic sample of the isomeric compound Se-(methylthio)selenocysteine. Selenium-specific NMR spectroscopic methods were developed to directly analyze the aqueous extracts of the hydrolyzed selenized yeast without derivatization or separation. Selenomethionine and S-(methylseleno)cysteine were identified by 77Se−1H HMQC−TOCSY experiments. Keywords: Selenized yeast; selenoamino acids; S-(methylseleno...

54 citations

Journal ArticleDOI
TL;DR: The long-sought pathway by which selenocysteyl-tRNA[Ser]Sec is synthesized in eukaryotes has been revealed and its formation under biological conditions has been demonstrated.
Abstract: The long-sought pathway by which selenocysteyl-tRNA[Ser]Sec is synthesized in eukaryotes has been revealed. Seryl-tRNA[Ser]Sec is O-phosphorylated and SecS, a pyridoxal phosphate-dependent protein, catalyzes the reaction of O-phosphoseryl-tRNA[Ser]Sec with monoselenophosphate to give selenocysteyl-tRNA[Ser]Sec . 1 H- 77 Se HMQC-TOCSY NMR spectroscopy has been developed to detect the selenium-containing amino acids present in selenized yeast after protease XIV digestion. An archived selenized yeast sample is found to contain the novel amino acid S-(methylseleno)cysteine in addition to selenomethionine. Arsenite and selenite react with GSH to form (GS) 2 AsSe−. The structure of this compound has been determined by EXAFS, 77 Se NMR and Raman spectroscopic and chromatographic studies. Its formation under biological conditions has been demonstrated.

9 citations


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Journal ArticleDOI
TL;DR: Uptake, translocation and Se speciation in wheat supplied with selenate or selenite, or both, were investigated in hydroponic experiments andSelenite was rapidly converted to organic forms in roots, with limited translocation to shoots, and Selenite uptake is an active process likely mediated, at least partly, by phosphate transporters.
Abstract: Selenite can be a dominant form of selenium (Se) in aerobic soils; however, unlike selenate, the mechanism of selenite uptake by plants remains unclear. Uptake, translocation and Se speciation in wheat (Triticum aestivum) supplied with selenate or selenite, or both, were investigated in hydroponic experiments. The kinetics of selenite influx was determined in short-term (30 min) experiments. Selenium speciation in the water-extractable fraction of roots and shoots was determined by HPLC-ICPMS. Plants absorbed similar amounts of Se within 1 d when supplied with selenite or selenate. Selenate and selenite uptake were enhanced in sulphur-starved and phosphorus-starved plants, respectively. Phosphate markedly increased K(m) of the selenite influx. Selenate and selenite uptake were both metabolically dependent. Selenite was rapidly converted to organic forms in roots, with limited translocation to shoots. Selenomethionine, selenomethionine Se-oxide, Se-methyl-selenocysteine and several other unidentified Se species were detected in the root extracts and xylem sap from selenite-treated plants. Selenate was highly mobile in xylem transport, but little was assimilated to organic forms in 1 d. The presence of selenite decreased selenate uptake and xylem transport. Selenite uptake is an active process likely mediated, at least partly, by phosphate transporters. Selenite and selenate differ greatly in the ease of assimilation and xylem transport.

587 citations

Journal ArticleDOI
TL;DR: The exploitation of genetic resources used in bioengineering strategies of plants is illuminating the function of sulfate transporters and key enzymes of the S assimilatory pathway in relation to Se accumulation and final metabolic fate, providing the basic framework by which to resolve questions relating to the essentiality of Se in plants.
Abstract: The chemical and physical resemblance between selenium (Se) and sulfur (S) establishes that both these elements share common metabolic pathways in plants. The presence of isologous Se and S compounds indicates that these elements compete in biochemical processes that affect uptake, translocation and assimilation throughout plant development. Yet, minor but crucial differences in reactivity and other metabolic interactions infer that some biochemical processes involving Se may be excluded from those relating to S. This review examines the current understanding of physiological and biochemical relationships between S and Se metabolism by highlighting their similarities and differences in relation to uptake, transport and assimilation pathways as observed in Se hyperaccumulator and non-accumulator plant species. The exploitation of genetic resources used in bioengineering strategies of plants is illuminating the function of sulfate transporters and key enzymes of the S assimilatory pathway in relation to Se accumulation and final metabolic fate. These strategies are providing the basic framework by which to resolve questions relating to the essentiality of Se in plants and the mechanisms utilized by Se hyperaccumulators to circumvent toxicity. In addition, such approaches may assist in the future application of genetically engineered Se accumulating plants for environmental renewal and human health objectives.

576 citations

Journal ArticleDOI
TL;DR: It is concluded that Se-yeast from reputable manufacturers is adequately characterised, of reproducible quality, and that there is no evidence of toxicity even at levels far above the EC tolerable upper intake level of 300 μg/d.
Abstract: Selenium-enriched yeast (Se-yeast) is a common form of Se used to supplement the dietary intake of this important trace mineral. However, its availability within the European Union is under threat, owing to concerns expressed by the European Community (EC) Scientific Committee on Food that Se-yeast supplements are poorly characterised and could potentially cause the build up of Se in tissues to toxic levels. The present review examines the validity of these concerns. Diagrams of the biosynthesis and metabolism of Se compounds show which species can be expected to occur in Se-yeast preparations. Se-yeast manufacture is described together with quality-control measures applied by reputable manufacturers. The way in which speciation of Se-yeast is achieved is explained and results on amounts of Se species in various commercial products are tabulated. In all cases described, selenomethionine is the largest single species, accounting for 54-74 % of total Se. Se-yeast is capable of increasing the activity of the selenoenzymes and its bioavailability has been found to be higher than that of inorganic Se sources in all but one study. Intervention studies with Se-yeast have shown the benefit of this form in cancer prevention, on the immune response and on HIV infection. Of about one dozen supplementation studies, none has shown evidence of toxicity even up to an intake level of 800 microg Se/d over a period of years. It is concluded that Se-yeast from reputable manufacturers is adequately characterised, of reproducible quality, and that there is no evidence of toxicity even at levels far above the EC tolerable upper intake level of 300 microg/d.

519 citations

Journal ArticleDOI
TL;DR: Key developments in the current understanding of Se in higher plants are reviewed and recent advances in the genetic engineering of Se metabolism are discussed, particularly for biofortification and phytoremediation of Se-contaminated environments.

486 citations

Journal ArticleDOI
TL;DR: Plants can play vital role in overcoming Se deficiency and Se toxicity in different regions of the world, hence, detailed mechanism of Se metabolism inside the plants is necessary for designing effective Se phytoremediation and biofortification strategies.
Abstract: Selenium (Se) is an essential micronutrient for humans and animals, but lead to toxicity when taken in excessive amounts. Plants are the main source of dietary Se, but essentiality of Se for plants is still controversial. However, Se at low doses protects the plants from variety of abiotic stresses such as cold, drought, desiccation and metal stress. In animals, Se acts as an antioxidant and helps in reproduction, immune responses, thyroid hormone metabolism. Selenium is chemically similar to sulfur, hence taken up inside the plants via sulfur transporters present inside root plasma membrane, metabolized via sulfur assimilatory pathway, and volatilized into atmosphere. Selenium induced oxidative stress, distorted protein structure and function, are the main causes of Se toxicity in plants at high doses. Plants can play vital role in overcoming Se deficiency and Se toxicity in different regions of the world, hence, detailed mechanism of Se metabolism inside the plants is necessary for designing effective Se phytoremediation and biofortification strategies.

484 citations