75Se Compounds

[⁷⁵Se]selenite was obtained from commercial sources or produced at the Research Reactor at the University of Missouri. Individual rats were injected with 50 μCi of [⁷⁵Se]selenite (~0.5 μg Se). L-[⁷⁵Se]SeMet (1.1 Ci/μmole) was obtained from Amersham. [⁷⁵Se]selenodiglutathione was synthesized from 2 mCi of [⁷⁵Se]selenite (63 μCi/μg Se), which were reduced with 5 mg ascorbate, oxidized with concentrated redistilled HN0₃ and then dried at 60oC. The resulting selenite (0.24 μmoles) was reduced with GSH on ice for 16 h at pH < 1.0, using a 4 GSH:1 Se stoichiometry. A sample was analyzed using a Dowex-Ni column, which showed that 97% of the applied ⁷⁵Se eluted after GSSG and thus was present as [⁷⁵Se]GSSeSG (36). [⁷⁵Se]selenobetaine (dimethylselenoacetate, SeBetaine) was synthesized from 2.5 mCi of [⁷⁵Se]selenite (70 μCi/μg Se) by borohydride reduction, and reacted with iodomethane to produce trimethylselenonium ion. After purification, the trimethylselenonium ion was pyrolyzed to form dimethylselenide, which was reacted with bromoacetic acid to form dimethylselenoacetate. Purification on SP-Sephadex resulted in >60% recovery as SeBetaine (37). [⁷⁵Se]selenate was prepared by oxidizing [⁷⁵Se]selenite with 30% H₂O₂. Following oxidation, complexation with 2, 3- diaminonaphthalene, a selenite-specific reaction, showed that <3% of the ⁷⁵Se remained as selenite. A Packard model 5650 refrigerated gamma counter with 3” KI crystal was used for ⁷⁵Se counting (60% efficiency for ⁷⁵Se).