Selenomethionine production

Sreenath, H. K., Bingman, C. A., Buchan, B. W., Seder, K. D., Burns, B. T., Geetha, H. V, et al. (2005). Protocols for production of selenomethionine-labeled proteins in 2-L polyethylene terephthalate bottles using auto-induction medium. Protein Expr. Purif. 40,256-267. 

Stols, L., Millard, C. S., Dementieva, I. and Doimetiy, M. I. (2004). Production of selenomethionine-labeled proteins in two-liter plastic bottles for structure determination. ]. Struct. Funct. Genomics 5, 95-102. 

LMW yeast Se compounds is given [46], It was assumed that adenosylselenoho-mocysteine (AdoSe-Hcy), which had been identil>ed in yeast by different authors [51, 63], could be a demethylation product of adenosylselenomethionine (AdoSe-Met). The latter compound is formed when selenomethionine enters the pathway of its S analog in enzymatic transmethylation. For the safe detection of AdoSe-Met, an LMW fraction of Se enriched yeast was obtained by homogenization of fresh cells and precipitation of proteins with HCIO4 at 0°C. The identification and/or conf>rmation of species observed by ion-pairing (IP) HPLC-ICP-MS was accomplished by spiking the samples with both commercial and laboratory-synthesized standards, and by electrospray (ES) MS. 

Plants absorb Se from soil primarily as selenate and translocate it to the chloroplast, where it follows the sulfur assimilation pathway. Se is reduced (enzymatically and non-enzymatically) to selenide, which reacts with serine to form selenocysteine (76). It can be further metabolized to selenomethionine (79) and methylated to form products such as. Se-methyl selenomethionine (89). Alternatively, selenocysteine-specific methyl transferase may form -methyl selenocysteine (83), allowing the plant to accumulate extraordinarily large amounts of Se. 

Se-enriched yeast is the most abundant commercially available source of supplemental Se, with at least a dozen products. Selenomethionine is reported to be the primary chemical form of Se in yeast. Because manufacturers of Se-enriched yeast do not adhere to a single production and/or quality standard, the form of Se probably varies considerably from product to product. 

Selenium enters the food chain mainly as selenomethionine from plants that take the element up from the soil but do not appear to use it. The soil content of selenium is highly variable and can be low in volcanic soils when soluble salts are leached out by ground water. Soils in parts of China and New Zealand are particularly low in selenium. Acid soils, where insoluble selenium complexes can be formed with iron and aluminum, occur in some parts of Europe, resulting in low available soil selenium. The geographical source of plant and animal foodstuffs determines the level of dietary intake. In the United States and Canada, wheat and other cereal products are a good source of selenium average intakes in North America range from 80 to 220 fig Se per day, whereas in the UK dietary intake is about 30 to 60 Llg/day. Intakes in China are as low as 11 lg/day and in New Zealand 28 fig/day. ... 

Reproductive Effects. In samples from more than 200 men, no correlation between seminal fluid selenium and sperm count or mobility was detected. No significant increase in spontaneous abortions was reported among women chronically exposed to drinking water containing excessive amounts of selenium. Oral or injection treatment of rats with sodium selenate or selenite (at doses at least 8 times greater than those normally supplied by an adequate diet) has been shown to increase the number of abnormal sperm, produce testicular hypertrophy, or degeneration and atrophy in males, and to affect the estrous cycle in females. The animals in these studies were not mated, so it is not clear if fertility was affected. A small increase in the number of abnormal length estrous cycles was observed in mice exposed to selenium. Disturbances in the menstrual cycle (anovulation, short luteal and follicular phases) were also observed in monkeys treated orally with L-selenomethionine. Selenium deficiency has also been reported to cause decreased sperm production and motility in rats. The relevance of these reproductive effects of selenium in laboratory animals to potential reproductive effects in humans is not known. 

Elemental selenium (selenium[0]) is rarely found naturally, but it is stable in soils. Selenates (selenium[+6]) and selenites (selenium[+4]) are water soluble and can be found in water. Sodium selenate is among the most mobile forms of selenium because of its high solubility and inability to adsorb to soil particles. More insoluble forms, such as elemental selenium, are less mobile therefore, there is less risk for exposure. Because of greater bioavailability, water-soluble selenium compounds are probably more lethal than elemental selenium by any route. Selenium is found in nature complexed with multiple compounds, and although various forms are discussed in the profile, many others exist. Plants can contain organic selenium in the form of the amino acids selenomethionine and selenocysteine, along with the dimethyl selenides. Elemental selenium can be oxidized to form selenium dioxide. While the products of oxidation might be expected at the soil surface, elemental selenium would be the expected predominant form in deep soils where anaerobic conditions exist. Selenium sulfides, used in some antidandruff shampoos, are not very water soluble and, therefore, like elemental selenium are relatively immobile in the environment. 

DL-Selenomethionine was initially synthesized by Painter" via a sodium/liquid ammonia reduction of DL-selenohomocystine followed by an alkylation of the resulting sodium selenohomocysteinate with methyl iodide. Other syntheses have since been reported including synthetic pathways for the preparation of optically active material" " and isotopically labeled material "" . DL-Selenomethionine has a solubility in water at 30° and pH 7 of 0.108 M which is considerably less than that for L-methionine (0.386 M). After seven hours of hydrolysis under anaerobic conditions in 6 N HCl at 110 °C selenomethionine is completely decomposed (under the same conditions 96% of methionine remains). Chemically, selenomethionine appears to be more reactive than methionine . For example, with cyanogen bromide, selenomethionine completely reacts in 0.1 M HCl in fifteen minutes while methionine requires twenty-four hours for the same reaction. In both cases the end product is homoserine. Although not as marked, this difference in reactivity was also confirmed in the reaction with hydrogen peroxide . 

Structure solutions do not always emerge easily and so there are a few approaches that may help in overcoming some of the problems of which perhaps the most notable is the production of heavy atom derivatives for solving the phase problem, [a] Selenomethionine can be introduced into the molecule by growing an... 

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