SEPHS1, also known as Selenophosphate synthetase 1, is a vital enzyme involved in the biosynthesis of selenoproteins, a class of proteins containing the amino acid selenocysteine (Sec). Positioned predominantly within the cytoplasm of cells, SEPHS1 plays a crucial role in selenium metabolism and the incorporation of selenocysteine into nascent selenoproteins. One of the primary functions of SEPHS1 is its involvement in the synthesis of selenophosphate, the activated form of selenium required for selenocysteine incorporation. As a selenophosphate synthetase, SEPHS1 catalyzes the conversion of selenide and ATP into selenophosphate, providing the essential precursor for selenocysteine tRNA (Sec-tRNA^[Ser]Sec) biosynthesis. Moreover, SEPHS1 is indispensable for...