Affiliations: Faculty of Pharmaceutical Sciences, Nagoya City University, Mizuho‐ku, Nagoya 467‐8603, Japan
Note: [] Corresponding author: T. Mizutani, Faculty of Pharmaceutical Sciences, Nagoya City University, Mizuho‐ku, Nagoya 467‐8603, Japan. Tel.: +81 52 836 3490; Fax: +81 52 834 9309; E‐mail: mizutani@ phar.nagoya‐cu.ac.jp.
Abstract: The mechanism of selenocysteine synthesis on tRNA^\mathrm{Sec }in mammals was previously studied by means of HSe^{-} as a Se donor to synthesize selenocysteine. It has been recently established that HSe^{-} in E. coli is activated by ATP to become selenophosphate (SeP). In this study, we provide evidence that [^{75}Se]selenocysteine is produced by bovine selenocysteine synthase from Ser‐tRNA^\mathrm{Sec} and [^{75}Se]SeP, synthesized from elemental ^{75}Se and Tris(trimethylsilyl)phosphite. We also studied the stability of SeP by NMR measurement. SeP was stable during storage under nitrogen at -80^\circC for 3 months in 0.2 M Hepes buffer at pH 6.8. However, SeP decomposed at 0^\circC in air (half life 32 hrs) or at 22^\circC under nitrogen (half life 30 hrs) at pH 6.8. The half lives of SeP at -19^\circC in air and at 0^\circC under nitrogen at pH 6.8 were 740 and 840 hrs, respectively. At pH 4 under nitrogen at 22^\circC, the half life was 240 hrs. The half life was only 9.2 hrs at pH 9 under nitrogen at 0^\circC. Thus, SeP was proved to be stable at low temperature, under acidic and anaerobic conditions, but labile under neutral and alkaline conditions.The LD_{50} of SeP administered i.p. to mice was 37.5 mg/kg body weight.
