Zachara B A
Department of Biochemistry, Medical School, Bydgoszcz, Poland.
J Trace Elem Electrolytes Health Dis. 1992 Sep;6(3):137-51.
Selenium (Se) is an essential trace element for animals and humans. Its biological role was established following the discovery that Se is a structural component of the active center of the enzyme glutathione peroxidase (GSH-Px). During the last decade remarkable progress has been made in the recognition of the structure and function of several selenoproteins. Cellular GSH-Px was the first enzyme recognized as a selenoprotein. In it Se was found in the form of selenocysteine. The enzyme is a tetrameric protein and is composed of four apparently identical subunits each containing one gram atom of Se. Plasma GSH-Px also has a tetrameric form with identical subunits and with one atom of Se per subunit. It is, however, a glycosylated protein, and is distinct from cellular enzyme. Both enzymes catalyze the reduction of hydrogen peroxide and a variety of organic hydroperoxides by glutathione. A third GSH-Px, called phospholipid hydroperoxide glutathione peroxidase (PHGSH-Px), is a monomeric, membrane-associated enzyme containing one atom of Se per mole of protein. This enzyme destroys esterified lipid hydroperoxides. The fourth known mammalian selenoenzyme is a type I iodothyronine 5'-deiodinase that catalyzes the deiodination of L-thyroxine to the biologically active hormone 3,3',5-triiodothyronine. It is a monomeric enzyme and contains one atom of Se per mole of protein. Selenoprotein P, a fifth known selenoprotein, is a glycosylated, monomeric protein containing ten atoms of Se per molecule. The function of this protein is not known, but it may play a role in Se transport or be connected with a protective activity against free radicals. In all these selenoproteins the Se is incorporated into the protein molecule via the selenocysteinyl-tRNA which recognizes the specific UGA codons in mRNAs to insert selenocysteine into the primary structure of selenoproteins.
硒（Se）是动物和人类必需的微量元素。在发现硒是谷胱甘肽过氧化物酶（GSH-Px）活性中心的结构成分之后，其生物学作用得以确立。在过去十年中，人们对几种硒蛋白的结构和功能的认识取得了显著进展。细胞谷胱甘肽过氧化物酶是首个被认定为硒蛋白的酶。在该酶中，硒以硒代半胱氨酸的形式存在。这种酶是一种四聚体蛋白，由四个明显相同的亚基组成，每个亚基含有一克原子的硒。血浆谷胱甘肽过氧化物酶也具有四聚体形式，其亚基相同，每个亚基含有一个硒原子。然而，它是一种糖基化蛋白，与细胞酶不同。这两种酶都通过谷胱甘肽催化过氧化氢和多种有机过氧化物的还原反应。第三种谷胱甘肽过氧化物酶，称为磷脂氢过氧化物谷胱甘肽过氧化物酶（PHGSH-Px），是一种单体的膜相关酶，每摩尔蛋白质含有一个硒原子。这种酶可破坏酯化的脂质过氧化物。已知的第四种哺乳动物硒酶是I型碘甲状腺原氨酸5'-脱碘酶，它催化L-甲状腺素脱碘生成具有生物活性的激素3,3',5-三碘甲状腺原氨酸。它是一种单体酶，每摩尔蛋白质含有一个硒原子。硒蛋白P是已知的第五种硒蛋白，是一种糖基化的单体蛋白，每个分子含有十个硒原子。这种蛋白质的功能尚不清楚，但它可能在硒的转运中发挥作用，或者与针对自由基的保护活性有关。在所有这些硒蛋白中，硒通过硒代半胱氨酰-tRNA掺入蛋白质分子，该tRNA识别mRNA中的特定UGA密码子，将硒代半胱氨酸插入硒蛋白的一级结构中。
