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Selenophosphate as a substrate for mammalian selenocysteine synthase, its stability and toxicity
Author(s) -
Mizutani Takaharu,
Kanaya Kazuo,
Tanabe Kazutaka
Publication year - 1999
Publication title -
biofactors
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.204
H-Index - 94
eISSN - 1872-8081
pISSN - 0951-6433
DOI - 10.1002/biof.5520090105
Subject(s) - atp synthase , chemistry , toxicity , biochemistry , enzyme , organic chemistry
The mechanism of selenocysteine synthesis on tRNA 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 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°C for 3 months in 0.2 M Hepes buffer at pH 6.8. However, SeP decomposed at 0°C in air (half life 32 hrs) or at 22°C under nitrogen (half life 30 hrs) at pH 6.8. The half lives of SeP at ‐19°C in air and at 0°C under nitrogen at pH 6.8 were 740 and 840 hrs, respectively. At pH 4 under nitrogen at 22°C, the half life was 240 hrs. The half life was only 9.2 hrs at pH 9 under nitrogen at 0°C. 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.