M.A. Beilstein

Bio: M.A. Beilstein is an academic researcher from Oregon State University. The author has contributed to research in topics: Selenocysteine & Sodium dodecyl sulfate. The author has an hindex of 3, co-authored 3 publications receiving 131 citations.

Glutathione peroxidase activity and chemical forms of selenium in tissues of rats given selenite or selenomethionine.

Abstract: Glutathione peroxidase (GPx) activity and deposition of selenium (Se) were examined in tissues of rats given dietary Se for 7 wk as either selenite or Selenomethionine (SeMet) with 75 Se radiotracer of the same chemical form On the basis of Se: 75 Se ratio, all tissues of the rats fed selenite were equilibrated with the dietary source, but tissues of the SeMet fed animals maintained a ratio of Se: 75 Se greater than the dietary ratio Deposition of dietary Se and 75 Se was higher in most tissues of rats fed SeMet Muscle 75 Se was the largest single tissue pool of 75 Se in both groups accounting for one-third of recovered 75 Se in the rats fed selenite, and one-half of recovered 75 Se in the rats fed SeMet Tissue GPx activities were not different between the two dietary groups The proportion of Se as GPx in tissues was highest in erythrocytes of the rats fed selenite (81) and lowest in testes and epididymides of the rats fed SeMet (009) The proportion of Se present in cytosolic GPx was consistently higher in tissues of rats fed selenite Erythrocytes of the rats fed SeMet had more 75 Se associated with hemoglobin, and muscle cytosols of the rats fed selenite had more 75 Se associated with the G-protein The proportion of 75 Se as SeMet determined by ion exchange chromatography of tissue hydrolysates was higher in tissues of rats fed SeMet (highest in muscle and hemoglobin, 70%, and lowest in testes, 16%) In contrast, selenocysteine was the predominant form of Se present in tissues of rats given selenite These results indicate that the form of Se administered will influence the form in the tissues, the percentage of Se with GPx and the body burden of Se

Evidence for selenocysteine in ovine tissue organelles

Abstract: Subcellular fractions were prepared by differential centrifugation from heart and liver of a lamb labeled with 75Se-selenite. Crude fractions of nuclei, mitochondria, and microsomes from both tissues were solubilized with sodium dodecyl sulfate and chromatographed on columns of sephacryl S-200. A low molecular weight (MW) 75Se labeled cardiac cytosol protein (approximately 10,000 daltons) was partially purified by gel filtration chromatography. The major 75Se peaks from the sephacryl columns and the low MW cardiac protein were hydrolyzed in HCl under an inert atmosphere. When chromatographed on an amino acid analysis column, 75Se from each hydrolysate chromatographed in the identical position of 2,7-diamino-4-thia-5-selenaoctanedioic acid, the mixed oxidized dimer of cysteine and selenocysteine. The low MW cardiac protein was reacted with chloroacetate after reduction with borohydride. 75Se from a hydrolysate of this derivatized protein eluted in the same position as Se-carboxymethylselenocysteine on the amino acid analysis column. Thus, selenocysteine appears to be the predominant form of selenium in ovine heart and liver.

Metabolism of selenomethionine and effects of interacting compounds by mammalian cells in culture.

Abstract: Since differences have been found in animals, the efficacies of selenomethionine (SeMet), selenite, and selenocystine (SeCys) for glutathione peroxidase (GPx) induction and cellular incorporation were compared and some effects of interacting nutrients on SeMet utilization were examined in tissue cultures. In three cell lines, Chang liver cells, mouse myoblasts and human fibroblasts, selenite was more effective than SeMet for GPx induction. However, radiotracer studies showed that SeMet was more rapidly incorporated into all cells than either selenite or SeCys. Chromatography of acid hydrolysates of Chang liver cells grown with 75Se-labeled SeMet indicated that approximately 90% of incorporated 75Se remained as SeMet, and less than 10% was as SeCys, the form of Se in GPx. Selenite supplementation slightly reduced both the incorporation of 75SeMet and the proportion of cellular 75Se recoverable as SeCys in Chang liver cells. Supplementation with L-methionine, however, significantly reduced 75SeMet incorporation, but significantly increased the proportion of cellular 75Se recovered as SeCys. L-cystine supplementation had no effect on either the cellular incorporation of 75SeMet or the proportion of cellular 75Se recovered as SeCys. These studies of SeMet utilization and effects of interacting nutrients are reflective of observations on SeMet metabolism in whole animals and humans.

Selenium and its relationship to cancer: an update.

Abstract: Selenomethionine (Semet) is the major seleno-compound in cereal grains and enriched yeast whereas Se-methylselenocysteine (SeMCYS) is the major seleno-compound in Se-accumulator plants and some plants of economic importance such as garlic and broccoli exposed to excess Se. Animals can metabolize both Semet and SeMCYS. Epidemiological studies have indicated an inverse relationship between Se intake and the incidence of certain cancers. Blood or plasma levels of Se are usually lower in patients with cancer than those without this disorder, but inconsistent results have been found with toenail-Se values and the incidence of cancer. There have been eight trials with human subjects conducted on the influence of Se on cancer incidence or biomarkers, and except for one, all have shown a positive benefit of Se on cancer reduction or biomarkers of this disorder. This is consistent with about 100 small-animal studies where Se has been shown to reduce the incidence of tumours in most of these trials. Se-enriched yeast is the major form of Se used in trials with human subjects. In the mammary-tumour model, SeMCYS has been shown to be the most effective seleno-compound identified so far in reduction of tumours. Several mechanisms have been proposed on the mechanism whereby Se reduces tumours. Even though SeMCYS was shown to be the most effective seleno-compound in the reduction of mammary tumours, it may not be the most effective seleno-compound for reduction of colon tumours.

Selenocompounds in Plants and Animals and their Biological Significance

Abstract: There are several selenocompounds in tissues of plants and animals. Selenate is the major inorganic selenocompound found in both animal and plant tissues. Selenocysteine is the predominant selenoamino acid in tissues when inorganic selenium is given to animals. Selenomethionine is the major selenocompound found initially in animals given this selenoamino acid, but is converted with time afterwards to selenocysteine. Selenomethionine is the major selenocompound in cereal grains, grassland legumes and soybeans. Selenomethionine can also be the major selenocompound in selenium enriched yeast, but the amount can vary markedly depending upon the growth conditions. Se-methylselenocysteine is the major selenocompound in selenium enriched plants such as garlic, onions, broccoli florets and sprouts, and wild leeks.

Which form is that? The importance of selenium speciation and metabolism in the prevention and treatment of disease

Abstract: The biological activity of selenium is dependent upon its speciation We aim to integrate selenium speciation and metabolism into a discussion of the mechanisms by which selenium exerts its biological activity First, we present the current status of selenium in the prevention of cancer, cardiovascular and neurodegenerative diseases with particular attention paid to the results of major chemoprevention trials involving selenium supplementation A comprehensive review of the current understanding of the metabolism of common dietary selenium compounds – selenite, selenomethionine, methylselenocysteine and selenocystine – is presented, with discussion of the evidence for the various metabolic pathways and their products The antioxidant, prooxidant and other mechanisms of the dietary selenium compounds have been linked to their disease prevention and treatment properties The evidence for these various mechanisms – in vitro, in cells and in vivo – is evaluated with emphasis on the selenium metabolites involved We conclude that dietary selenium compounds should be considered prodrugs, whose biological activity will depend on the activity of the various metabolic pathways in, and the redox status of, cells and tissues These factors should be considered in future laboratory research and in selecting selenium compounds for trials of disease prevention and treatment by selenium supplementation

Selenium in biology and medicine

Abstract: In July, 1988, more than 300 scientists from 29 different countries gathered at Tiibingen, W. Germany, in order to spend 4 days discussing their favourite trace element, selenium. This meeting continued the good tradition of three previous meetings held in Corvallis/Oregon, 1976, in Lubbock/Texas, 1980, and in Beijing/China, in 1984. Incidentally, the University of Tiibingen provided a unique historical background for a Symposium devoted to recent advances in biochemistry, pharmacology, human nutrition and human health; here, the first independent depart ment of Physiological Chemistry in Germany was founded in 1845. Pro fessor H9Ppe-Seyler elucidated here the hemin structure and his student Friedrich Miescher discovered the nucleic acids. This book contains one-half of the oral or poster presentations which were selected before the meeting was held on the basis of a one page abstract. It is the reader who will have to decide whether this time consuming policy of quality assessment was warranted or not."