硒代氨基酸代谢
中文名称
通路描述
硒（Se）是人体正常功能所必需的微量元素。硒代氨基酸是指硒取代了硫的氨基酸。硒和硫具有许多化学性质相似，因此用硒代氨基酸取代正常氨基酸对蛋白质结构和功能的影响很小。无机（亚硒酸，SeO3(2-)；和亚硒酸根，SeO4(2-)）和有机（硒代蛋氨酸，Sec；和硒代半胱氨酸，SeMet）形式的硒可以通过饮食引入，并在磷酸化中间体的作用下，通过 tRNA 依赖性方式转化为中间态硒化物（Se(2-)），然后用于从头合成 Sec。Sec 的形成最终步骤由 O-磷酸硒酰-tRNA：硒代半胱氨酸-tRNA 合成酶（SEPSECS）催化，将磷酸硒酰-tRNA(Sec)转化为硒代半胱氨酸-tRNA(Sec)。所有营养性硒都被代谢为硒化物，或者通过甲基硒醇（MeSeH）代谢。从硒蛋白中释放的 Sec 由硒代蛋氨酸裂解酶（SCLY）转化为 Se(2-)。从一般蛋白质和游离硒代半胱氨酸来源中释放的 SeMet 通过 CTH 催化转化为 MeSeH，然后脱甲基（SeMet 到 CH3SeH 到 H2Se），或者通过转硒化途径（SeMet 到 Sec 到 H2Se）由 SCLY 转化为 Se(2-)。MeSec 由 CTH 水解为 MeSeH。甲基硒inic 酸（MeSeO2H）被还原为甲基硒醇。MeSeH 被脱甲基为 Se(2-)，用于进一步合成硒蛋白或氧化为亚硒酸（SeO3(2-)）以以硒糖的形式排出体外。此外，MeSeH 进一步甲基化为二甲基硒化物（Me2Se）和三甲基硒阳离子（Me3Se+）以排出体外。
英文描述
Selenoamino acid metabolism Selenium (Se) is a trace element essential for the normal function of the body. Selenoamino acids are defined as those amino acids where selenium has been substituted for sulphur. Selenium and sulphur share many chemical properties and so the substitution of normal amino acids with selenoamino acids has little effect on protein structure and function. Both inorganic (selenite, SeO3(2-); and selenate, SeO4(2-)) and organic (selenocysteine, Sec; and selenomethionine, SeMet) forms of selenium can be introduced in the diet where they are transformed into the intermediate selenide (Se(2-)) and then utilized for the de novo synthesis of Sec through a phosphorylated intermediate in a tRNA-dependent fashion. The final step of Sec formation is catalyzed by O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase (SEPSECS) that converts phosphoseryl-tRNA(Sec) to selenocysteinyl-tRNA(Sec).
All nutritional selenium is metabolised into selenide directly or through methylselenol (MeSeH). Sec liberated from selenoproteins is transformed to Se(2-) by selenocysteine lyase (SCLY). SeMet liberated from general proteins and from free SeMet sources is transformed into Se(2-) either through MeSeH by cystathionine gamma-lyase (CTH) followed by demethylation (SeMet to CH3SeH to H2Se), or through Sec by SCLY after the trans-selenation pathway (SeMet to Sec to H2Se). MeSec is hydrolysed into MeSeH by CTH. Methylseleninic acid (MeSeO2H) is reduced to methylselenol. MeSeH is demethylated to Se(2-) for further utilization for selenoprotein synthesis or oxidised to selenite (SeO3(2-)) for excretion in the form of selenosugar. Additionally, MeSeH is further methylated to dimethylselenide (Me2Se) and trimethylselenonium (Me3Se+) for excretion.
All nutritional selenium is metabolised into selenide directly or through methylselenol (MeSeH). Sec liberated from selenoproteins is transformed to Se(2-) by selenocysteine lyase (SCLY). SeMet liberated from general proteins and from free SeMet sources is transformed into Se(2-) either through MeSeH by cystathionine gamma-lyase (CTH) followed by demethylation (SeMet to CH3SeH to H2Se), or through Sec by SCLY after the trans-selenation pathway (SeMet to Sec to H2Se). MeSec is hydrolysed into MeSeH by CTH. Methylseleninic acid (MeSeO2H) is reduced to methylselenol. MeSeH is demethylated to Se(2-) for further utilization for selenoprotein synthesis or oxidised to selenite (SeO3(2-)) for excretion in the form of selenosugar. Additionally, MeSeH is further methylated to dimethylselenide (Me2Se) and trimethylselenonium (Me3Se+) for excretion.
所含基因
11 个基因