Serine incorporation into the selenocysteine moiety of glutathione peroxidase.
The selenium in mammalian glutathione peroxidase is present as a selenocysteine ([Se]Cys) moiety incorporated into the peptide backbone 41-47 residues from the N-terminal end. To study the origin of the skeleton of the [Se]Cys moiety, we perfused isolated rat liver with 14C- or 3H-labeled amino acids for 4 h, purified the GSH peroxidase, derivatized the [Se]Cys in GSH peroxidase to carboxymethylselenocysteine ([Se]Cys(Cm)), and determined the amino acid specific activity. Perfusion with [14C]cystine resulted in [14C]cystine incorporation into GSH peroxidase without labeling [Se]Cys(Cm), indicating that cysteine is not a direct precursor for [Se]Cys. [14C]Serine perfusion labeled serine, glycine (the serine hydroxymethyltransferase product), and [Se]Cys(Cm) in purified GSH peroxidase, whereas [3-3H]serine perfusion only labeled serine and [Se]Cys(Cm), thus demonstrating that the [Se]Cys in GSH peroxidase is derived from serine. The similar specific activities of serine and [Se]Cys(Cm) strongly suggest that the precursor pool of serine used for [Se] Cys synthesis is the same or similar to the serine pool used for acylation of seryl-tRNAs.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002250:Carbon Radioisotopes; D003545:Cysteine / Q000031:analogs & derivatives* / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000096:biosynthesis* / Q000302:isolation & purification; D008099:Liver / Q000201:enzymology*; D008297:Male; D011868:Radioisotopes; D051381:Rats; D012643:Selenium / Q000378:metabolism*; D017279:Selenocysteine; D012694:Serine / Q000378:metabolism*; D014316:Tritium
D000596:Amino Acids; D002250:Carbon Radioisotopes; D011868:Radioisotopes; D017279:Selenocysteine; D014316:Tritium; D012694:Serine; D005979:Glutathione Peroxidase; D012643:Selenium; D003545:Cysteine