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ARS Home » Research » Publications at this Location » Publication #99190
Title: SYNTHESIS AND STRUCTURE CHARACTERIZATION OF SELENIUM METABOLITES

Author
item FAN, T - UNIV. OF CALIFORNIA, CA
item LANE, A - MOLECULAR STRUCT., LONDON
item Martens, Dean
item HIGASHI, R - UNIV. OF CALIFORNIA, CA

Submitted to: Analyst
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Selenium is an essential micronutrient, however, high levels can cause reproductive failure in animals. It was discovered in the Central Valley of California in the early 1980's that irrigation drainage water contained high enough levels of Selenium to cause deformations in water fowl who used these drainage ponds for nesting sites. Selenium problems resulting from agricultural practices have been reported in other semi-arid areas in the west from Montana, New Mexico, and California. Selenium from irrigation drainage water is present in the inorganic form and is changed into organic forms through microorganisms and plants. It is the organic form that causes problems with reproduction in animals. One of the major limitations to understanding the role of Selenium is the lack of understanding of the pathways that inorganic Selenium is converted to organic Selenium and the intermediate forms. Some of these intermediate forms of Selenium were made in the laboratory in an attempt to understand these natural pathways. As a result of these studies it is now possible to manage irrigation waters to reduce the amount of organic Selenium present in the environment and reduce the impact of high organic Selenium concentrations on animal reproduction. These methods provide a new understanding of the biological processes linked with Selenium in the environment that reduces the potential toxicity of this nutrient.

Technical Abstract: The difficulty in analyzing trace-level organoseleno metabolites and the lack of commercially available standards have been major barriers to a molecular-level understanding of Se biogeochemistry, ecotoxicology, and nutrition, particularly in aquatic ecosystems. To overcome the problem, we synthesized three important precursors of volatile alkylselenides including gdimethylselenonium propionate (DMSeP) which has only been postulated to exist in nature. A combination of 2-D multinuclear NMR, electrospray-MS and GC-MS methods were employed to identify DMSeP, methylselenomethionine, and methylselenocysteine in synthetic preparations without extensive cleanup. An alkaline hydroelimination test coupled with GC-MS analysis for the release pattern of dimethylselenide (DMSe) and dimethyldiselenide (DMDSe) was developed for determination of the three products. The DMSe release pattern of DMSeP confirmed the presence of a DMSeP-like compound in the biomass of 100 mg/L Se-treated Chlorella investigated previously. Silylation/GC-MS was tested for the analysis of selenomethionine, selenocysteine, and methylselenocysteine in a standard mixture with a detection limit of better than one pmole per 0.5 microliter injection volume. This method was applied to the analysis of the acid digest of the proteinaceous fraction of the Chlorella culture. Selenomethionine was found to contain greater than 70 percent of the protein-bound Se, although this constituted only a minor fraction of the total Se in the Chlorella biomass. These findings revealed the metabolic relationship between Se volatilization and selenomethionine incorporation into proteins. This knowledge is critical to the advancement in Se biogeochemistry, ecotoxicology, and the development of bioremediation schemes.