Biosynthesis, Properties, and Functions of Selenoenzymes and Seleno-tRNAs

硒磷酸合成酶形成能量丰富的 从三磷酸腺苷和硒化物中提取的化合物，硒磷酸盐。必需品 大肠杆菌酶中的半胱氨酸残基被硒半胱氨酸取代， 苏氨酸，或精氨酸，在各种真核形式的酶。 这些取代物的相对催化活性 已评估。游离硒在体外不能作为底物。 苏氨酸和精氨酸取代酶。另外，相对的 S酶和Se酶对硒的低活性表明 另一种形式的硒应该是体内的底物。硫磺 通常从酶中输送活性硫的转移酶 过硫化物中间体也可以作为硒的输送系统。 在体外，从而取代了毒性很大的游离硒。然而， 已知的硒专一性酶，如L-硒半胱氨酸裂解酶， 应该可以在活体内发挥作用。硒半胱氨酸的初步纯化步骤 裂解酶和硒磷酸合成酶同工酶 潜在丰富的厌氧菌源被开发出来。这个 来自万尼氏甲烷球菌的磷酸硒合成酶显示 与已知形式的酶有显著的序列差异。 猪瘟病毒野生型和突变型的机理研究 来自大肠杆菌的磷酸硒合成酶表明，磷酸化 ATP对酶的作用不受影响。进一步试图描绘出 磷酸化位点正在进行中。酶的三种形式 通过去除C端的多肽而减少质量 通过诱变产生不同长度的DNA。鉴于 低谷胱甘肽与硒缺乏的相关性观察 艾滋病毒感染者存活率较低的水平，是 有兴趣研究T细胞中的硒代谢。一种新的合成方法 用75-Se标记人Jurkat T细胞的硒蛋白 人类免疫缺陷病毒感染的标记蛋白及其图谱的研究 与未感染的T细胞进行比较。

Selenophosphate synthetase forms the energy-rich compound, selenophosphate, from ATP and selenide. An essential cysteine residue in the E. coli enzyme is replaced by selenocysteine, threonine, or arginine in various eukaryotic forms of the enzyme. The relative catalytic activities of these replacements have been evaluated. Free selenide is inactive as substrate in vitro for the threonine- and arginine-substituted enzymes. Also, the relatively low activities of the S and Se enzymes on selenide indicated that another form of selenium should be the in vivo substrate. Sulfur transferases that normally deliver active sulfur from enzyme persulfide intermediates also can serve as selenium delivery systems in vitro, thus replacing free selenide, which is very toxic. However, known selenium-specific enzymes, such as L-selenocysteine lyase, should function in vivo. Initial purification steps for selenocysteine lyases and also selenophosphate synthetase isoenzymes from two potentially rich anaerobic bacterial sources were developed. The selenophosphate synthetase from Methanococcus vannielii shows significant sequence differences from known forms of the enzyme. Mechanistic studies on wild type and mutant forms of selenophosphate synthetase from E. coli show that phosphorylation of enzyme by ATP is unaffected. Further attempts to delineate the phosphorylation site are in progress. Three forms of the enzyme that were decreased in mass by removal of C-terminal peptides of varying lengths were produced by mutagenesis. In view of the observed correlations of selenium deficiency and low glutathione levels with poor survival of HIV-infected individuals, it was of interest to study selenium metabolism in T cells. Synthesis of 75-Se-labeled selenoproteins by human Jurkat T cells was investigated and the profiles of labeled proteins from HIV-infected and uninfected T cells were compared.