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

硒磷酸合成酶形成富含能量的 化合物，硒磷酸盐，从ATP和硒化物。一个基本 E.大肠杆菌酶被硒代半胱氨酸取代， 苏氨酸或精氨酸。 这些替代物的相对催化活性已被证明是 评估。游离硒化物在体外作为底物是无活性的， 苏氨酸和苏氨酸取代的酶。此外，相对 低活性的S和Se酶对硒化物的指示， 另一种形式的硒应该是体内底物。硫 通常从酶传递活性硫的转移酶 过硫化物中间体也可以作为硒的传递系统 从而取代毒性很大的游离硒化物。然而，在这方面， 已知的硒特异性酶，例如L-硒代半胱氨酸裂解酶， 应该在体内发挥作用。硒代半胱氨酸的初始纯化步骤 裂合酶和硒磷酸合成酶同工酶， 开发了潜在丰富的厌氧细菌源。的 来自范氏甲烷球菌的硒磷酸合成酶显示 与已知形式的酶的显著序列差异。 野生型和突变型的机制研究 硒磷酸合成酶。大肠杆菌中发现磷酸化 ATP对酶的影响不受影响。进一步尝试描绘 磷酸化位点正在进行中。酶的三种形式 通过去除C-末端肽， 通过诱变产生不同的长度。考虑到 观察到硒缺乏和低谷胱甘肽的相关性 艾滋病毒感染者的生存率很低， 研究硒在T细胞中代谢的兴趣。合成 75-Se标记的人Jurkat T细胞的硒蛋白， 研究和标记的蛋白质从艾滋病毒感染者的概况， 和未感染的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.