Failure of selenomethionine residues in albumin and immunoglobulin G to protect against peroxynitrite

Selenomethionine has been suggested to protect against peroxynitrite by que nching it in vivo. Selenomethionine is distributed randomly in the methioni ne pool. Albumin and IgG were purified from plasma of a human being before and after 28 days of supplementation with 400 mu g selenium/day as selenome thionine. The albumin contained 1 selenium atom, presumably as selenomethio nine, per 8000 methionine residues before supplementation and 1 per 2800 af ter supplementation. Although this ratio suggested that selenomethionine wo uld not have as great an effect in quenching peroxynitrite as would methion ine, direct testing of the albumin and IgG; fractions was carried out to as sess the ability of these proteins to prevent peroxynitrite oxidation of di hydrorhodamine 123 to rhodamine 123. The ability of the albumin preparation s to resist nitration of tyrosine residues was also assessed. The high-sele nomethionine preparations of the proteins had no greater effect in quenchin g the peroxynitrite than did the normal-selenomethionine preparations. Thes e results do not support the proposal that selenomethionine in proteins con tributes to in vivo protection against peroxynitrite. (C) 1999 Academic Pre ss.