Burk R F, Hill K E
Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232.
J Nutr. 1994 Oct;124(10):1891-7. doi: 10.1093/jn/124.10.1891.
Selenoprotein P is a glycoprotein that has been purified from rat and human plasma. In selenium-replete rats it contains 65% of the plasma selenium and its concentration is 25-30 mg protein/L. In selenium-deficient rats its concentration is < 3 mg protein/L. The plasma half life of 75Se in selenoprotein P is 3 to 4 h, indicating a rapid turnover. Purified rat selenoprotein P contains 7.5 +/- 1 selenium atoms per molecule as selenocysteine. The sequence of the cloned cDNA predicts 10 selenocysteine residues, which suggests that the protein in plasma is a modification of the predicted one. Deduced amino acid sequence identity between rats and humans is 72%. The 3' untranslated region of selenoprotein P cDNA contains two predicted stem loops of the type essential for selenocysteine incorporation. Northern analysis indicates that selenoprotein P is expressed by many tissues. Hepatic selenoprotein P mRNA level, but not its transcription, decreases during selenium deficiency. The decrease is less than the decrease of glutathione peroxidase mRNA, however. Selenoprotein P is postulated to serve as an extracellular oxidant defense because its presence correlates with selenium protection of selenium-deficient rats against diquat-induced lipid peroxidation and liver necrosis. More research will be required to test this hypothesis and to establish the biochemical function of selenoprotein P.
硒蛋白P是一种已从大鼠和人血浆中纯化出来的糖蛋白。在硒充足的大鼠中，它含有65%的血浆硒，其浓度为25 - 30毫克蛋白质/升。在缺硒大鼠中，其浓度<3毫克蛋白质/升。硒蛋白P中75Se的血浆半衰期为3至4小时，表明其周转迅速。纯化的大鼠硒蛋白P每个分子含有7.5±1个作为硒代半胱氨酸的硒原子。克隆的cDNA序列预测有10个硒代半胱氨酸残基，这表明血浆中的蛋白质是预测蛋白质的一种修饰形式。大鼠和人之间推导的氨基酸序列同一性为72%。硒蛋白P cDNA的3'非翻译区含有两个预测的对硒代半胱氨酸掺入至关重要的茎环结构。Northern分析表明硒蛋白P在许多组织中表达。在硒缺乏期间，肝脏硒蛋白P的mRNA水平下降，但其转录水平不变。然而，这种下降小于谷胱甘肽过氧化物酶mRNA的下降。硒蛋白P被认为可作为一种细胞外抗氧化防御物质，因为它的存在与缺硒大鼠对百草枯诱导的脂质过氧化和肝坏死的硒保护作用相关。需要更多的研究来验证这一假设并确定硒蛋白P的生化功能。
