T9 AM Bioaccumulation and Biomagnification
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 339-340

(UNR-1117-729565) Use of hyphenated analytical techniques to describe the macromolecular distribution of selenium in reptilian tissues.

Unrine, J¹, Jackson, B², Hopkins, W³, Romanek, C^{1, 4}, ¹ The University of Georgia , Savannah River Ecology Laboratory, Aiken, SC, USA² Dartmouth College, Hanover, NH, USA³ Virginia Polytechnic Institute and State University, Blacksburg, VA, USA⁴ The University of Georgia, Department of Geology, Athens, GA, USA

ABSTRACT- Selenium (Se) is an essential trace element which is chemically analogous to sulfur (S) that becomes toxic at elevated tissue concentrations. The mode of action for Se toxicity is thought to involve substitution for S in the amino acids cysteine, cystine, and methionine. It has been hypothesized that this substitution may alter the tertiary structure of proteins though disruption of normal disulfide bonding. We investigated the distribution of Se in proteins relative to the distribution of S in western fence lizards (Sceloporus occidentalis) exposed to dietary Se using size exclusion chromatography dynamic reaction cell quadrupole inductively coupled plasma mass spectrometry (SEC-DRC-ICP-MS). Use of a reaction cell pressurized with hydrogen (H) in tandem with the quadrupole ICP-MS enabled us to suppress molecular interferences (⁴⁰Ar⁴⁰Ar) so that ⁸⁰Se, the most abundant isotope of Se, could be used for sensitive detection of Se containing proteins. The reaction cell also significantly suppressed ¹⁶O¹⁸O interferences such that S content of proteins could be quantified using ³⁴S. We analyzed Se and S content of proteins from livers, testes, follicles, and eggs. We found that in all tissues Se content of proteins was highly dependent on S content. A previous study demonstrated that female lizards partitioned a greater percentage of their Se body burden to gonadal tissue than males. We hypothesized that this may be related to the macromolecular distribution of Se in these tissues. Sex related differences in Se distribution among proteins were evident in reproductive tissues, while differences in liver tissues were subtle or non-existent. The results help explain sex related differences in relative partitioning of Se based on the normal distribution of S in proteins from various tissues. Future studies will focus on identification of selenium containing proteins to understand the mechanisms of Se toxicity and maternal transfer.

Key words: Selenium, Size exclusion chromatography, ICP-MS, Protein