Werner E R, Werner-Felmayer G, Mayer B
Institute for Medical Chemistry and Biochemistry, University of Innsbruck, Innsbruck, Austria.
Proc Soc Exp Biol Med. 1998 Dec;219(3):171-82. doi: 10.3181/00379727-219-44331.
Nitric oxide synthases require a surprisingly rich selection of cofactors to perform the conversion of L-arginine to citrulline and nitric oxide (NO): NADPH, FAD, FMN, heme and tetrahydrobiopterin. In a previous minireview in this journal we summarized work concerning the induction of tetrahydrobiopterin biosynthesis by cytokines, which yields increased intracellular tetrahydrobiopterin concentrations supporting NO formation by intact cells (P.S.E.B.M. 203:1-12). The present review updates work on the induction of tetrahydrobiopterin biosynthesis by cytokines, and summarizes recent advances in research of tetrahydrobiopterin dependence of the NO synthase reaction. Studies using recombinant NO synthases and site-directed mutations thereof have localized several amino acids critical for tetrahydrobiopterin binding, which are discussed in reference to the recently published crystal structure of the dimer of the oxygenase domain of murine inducible NO synthase with substrate and pterin. Allosteric actions of tetrahydrobiopterin on NO synthases are stabilization of dimers, stabilization of a conformation with high-spin heme iron, and support of binding of the substrate L-arginine. Since the 4-amino analog of tetrahydrobiopterin, which is a dihydropteridine reductase inhibitor, supports these allosteric actions but inhibits the enzyme activity, tetrahydrobiopterin appears to play a redox-active role in stimulating the NO synthase reaction in addition to its allosteric actions on NO synthases. Amelioration of endothelial dysfunction by tetrahydrobiopterin in animal models and in humans in vivo has been observed. It remains to be investigated, however, to what extent the role of tetrahydrobiopterin as cofactor of NO synthases contributes to these in vivo effects of tetrahydrobiopterin.
一氧化氮合酶需要种类惊人丰富的辅助因子来完成将L-精氨酸转化为瓜氨酸和一氧化氮（NO）的过程：烟酰胺腺嘌呤二核苷酸磷酸（NADPH）、黄素腺嘌呤二核苷酸（FAD）、黄素单核苷酸（FMN）、血红素和四氢生物蝶呤。在本杂志之前的一篇小型综述中，我们总结了有关细胞因子诱导四氢生物蝶呤生物合成的研究工作，该过程会使细胞内四氢生物蝶呤浓度升高，从而支持完整细胞生成NO（《实验生物学与医学联合会会刊》203:1 - 12）。本综述更新了关于细胞因子诱导四氢生物蝶呤生物合成的研究工作，并总结了四氢生物蝶呤对一氧化氮合酶反应依赖性研究的最新进展。使用重组一氧化氮合酶及其定点突变体的研究已经确定了几个对四氢生物蝶呤结合至关重要的氨基酸，这些氨基酸将结合最近发表的小鼠诱导型一氧化氮合酶加氧酶结构域二聚体与底物和蝶呤的晶体结构进行讨论。四氢生物蝶呤对一氧化氮合酶的变构作用包括稳定二聚体、稳定高自旋血红素铁的构象以及支持底物L-精氨酸的结合。由于四氢生物蝶呤（一种二氢蝶呤还原酶抑制剂）的4-氨基类似物支持这些变构作用但抑制酶活性，因此四氢生物蝶呤除了对一氧化氮合酶具有变构作用外，似乎在刺激一氧化氮合酶反应中还发挥着氧化还原活性作用。在动物模型和人体中，已经观察到四氢生物蝶呤可改善内皮功能障碍。然而，四氢生物蝶呤作为一氧化氮合酶辅助因子的作用在多大程度上促成了四氢生物蝶呤的这些体内效应，仍有待研究。
