Selenium Biochemistry

硒磷酸盐（SeP）是由硒磷酸合成酶（SPS）与无机形式的硒（Se）反应生成的，是合成多种硒酶所必需的高能硒化合物。专门的硒递送蛋白的参与提供硒特异性SPS用于维持细胞内硒水平低于毒性水平。可以利用硒代半胱氨酸作为底物的某些类型的递送蛋白，硒代半胱氨酸裂解酶，包括来自大肠杆菌的三种NifS相关蛋白。大肠杆菌中的一种和来自范氏甲烷球菌（Methanococcus vannielii）的一种，范氏甲烷球菌是一种厌氧生物，其特别富含硒酶和硒蛋白生物合成所需的因子。 从M. vannielii。分离、克隆了编码该蛋白的基因，并在E. William Self博士的研究。表达的蛋白质，获得良好的产量和相同的天然蛋白质，结合亚硒酸盐。该蛋白的抗体使其易于从M. vannieli粗提物。迄今为止，在哺乳动物或细菌系统中均未发现高度氧不稳定的硒磷酸盐的稳定形式或加合物。这种一般的硒供体化合物必须在需要的地方就地合成，或者应该存在某种可运输的形式。根据我们先前制备的硫代磷酸酯-甲萘醌加成产物的性质，可能存在相应的硒代磷酸酯衍生物。劳拉坎贝尔博士正在研究一种独特的甲萘醌依赖性对硝基苯基磷酸酶在其形成中发挥作用的可能性。这种酶在某些富硒厌氧菌中相对丰富，没有已知的生物学功能。 作为对人类硫氧还蛋白还原酶研究的继续，Shoshana Bar-Noy博士测试了产生C-末端延伸的可行性，以允许将活性含硒半胱氨酸的酶与过早终止的非活性形式分离。不幸的是，Bar-Noy博士完成了她在NIH的允许逗留，并于2002年6月1日离开实验室，没有完成该项目。 存在于某些厌氧细菌中的一组硒依赖性嗜硒蝶呤羟化酶含有未鉴定的硒辅因子形式。由William Self博士发现和研究的嘌呤羟化酶是研究这种硒辅因子的极好系统，特别是关于其合成模式和添加到这些酶中的机制。模型供体化合物，如硫辛酸-硒加合物，由Self博士制备并测试。 由Gerard Lacourciere博士发起的一项关于各种硒传递蛋白的合作研究工作，这些蛋白被其他研究人员检测为细菌基因产物，在Lacourciere博士于2002年4月12日离开NIH后，Matt Wolfe博士继续进行。这些特征在于能够为硒磷酸合成酶提供原子硒以及与酶的相互作用类型。

Selenophosphate (SeP), the energy-rich Se compound required for synthesis of many selenoenzymes is formed by selenophosphate synthetase (SPS) from ATP and an inorganic form of Se. The participation of specialized selenium delivery proteins to furnish Se specifically to SPS serves to maintain intracellular levels of selenium below toxic levels. Certain classes of delivery proteins that can utilize selenocysteine as substrate, selenocysteine lyases, include three NifS related proteins from E. coli and one from Methanococcus vannielii, an anaerobic organism that is particularly rich in selenoenzymes and factors required for selenoprotein biosynthesis. A selenium-binding protein that reacts with inorganic selenium also was isolated from M. vannielii. The gene encoding this protein was isolated, cloned, and expressed in E. coli by Dr. William Self. The expressed protein, obtained in good yield and identical to native protein, binds selenite. Antibodies to this protein allow its ready isolation from M. vannielii crude extracts. To date no stabilized forms or adducts of the highly oxygen-labile selenophosphate have been found either in mammalian or bacterial systems. Either this general selenium donor compound must be synthesized in situ wherever needed or some transportable form should exist. Based on properties of a thiophosphate-menadione addition product that we prepared previously, a corresponding derivative of selenophosphate might exist. The possibility that a unique menadione-dependent paranitrophenyl phosphatase could have a role in its formation is being examined by Dr. Lara Campbell. This enzyme is relatively abundant in certain selenium-rich anaerobic bacteria and has no known biological function. As a continuation of studies on human thioredoxin reductase, Dr. Shoshana Bar-Noy tested the feasibility of producing C-terminal extensions to allow separation of the active selenocysteine-containing enzyme from prematurely terminated inactive forms. Unfortunately, Dr. Bar-Noy completed her allowed stay at NIH and left the laboratory on June 1, 2002, without finishing the project. A group of selenium-dependent molybdopterin hydroxylases present in some anaerobic bacteria contain an unidentified cofactor form of selenium. A purine hydroxylase discovered and studied by Dr. William Self is an excellent system for study of this selenium cofactor, particularly as regards its mode of synthesis and mechanism of addition to these enzymes. Model donor compounds, such as a lipoic acid-selenium adduct, are prepared by Dr. Self and tested. A collaborative research effort initiated by Dr. Gerard Lacourciere on various selenium delivery proteins that are detected as bacterial gene products by other investigators was continued by Dr. Matt Wolfe after Dr. Lacourciere left NIH on April 12, 2002. These are characterized as to ability to furnish atomic selenium for selenophosphate synthetase and types of interactions with the enzyme.