6,6-DIMETHYLPTERINS - STABLE QUINOID DIHYDROPTERIN SUBSTRATE FOR DIHYDROPTERIDINE REDUCTASE AND TETRAHYDROPTERIN COFACTOR FOR PHENYLALANINE-HYDROXYLASE
6,6-DIMETHYLPTERINS - STABLE QUINOID DIHYDROPTERIN SUBSTRATE FOR DIHYDROPTERIDINE REDUCTASE AND TETRAHYDROPTERIN COFACTOR FOR PHENYLALANINE-HYDROXYLASE
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DOI：
10.1021/bi00277a008
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发表时间：
1983-01-01
期刊：
影响因子：
2.9
通讯作者：
AYLING, JE
中科院分区：
文献类型：
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作者：
BAILEY, SW;AYLING, JE
芳香族氨基酸羟解酶的辅因子产物奎宁二氢生物蝶呤的互变异构体结构尚不清楚。该分子也是[绵羊肝脏]二氢蝶呤还原酶的底物，由于奎宁类二氢蝶呤类化合物快速重排为7，8-二氢蝶呤类化合物，该分子的特性受到阻碍。这种互变异构化可以通过6位的二取代来防止。报道了以邻二胺和2-氨基-6-氯-4(3H)-嘧啶酮为原料合成6，6-二取代蝶呤的方法。以6，6-二甲基四氢蝶呤(6，6-Me2PH4)的具体合成为例说明了该方法的可行性。6，6-Me2PH4是大鼠肝脏苯丙氨酸羟化酶的辅因子，其酶动力学参数与其位置异构体6，7-二甲基四氢蝶呤的酶动力学参数相似。所得化合物Q-6，6-二甲基二氢蝶呤(Q-6，6-Me2PH2)在0.1MTris-HCl中的半衰期分别为27和37度。C分别为4h和1.25h。Q-6，6-Me2PH2由苯丙氨酸羟基酶或6，6-Me2PH4化学氧化产生，是二氢蝶呤还原酶的底物，其Km值为0.4 mm，Vmax是奎宁类二氢生物蝶呤天然异构体的两倍。在0.4 mM以下，Q-6，6-Me2PH2对苯丙氨酸羟化酶无抑制作用，而6-甲基-7，8-二氢蝶呤和7，8-二氢生物蝶呤对苯丙氨酸羟化酶有竞争性抑制作用，其Ki分别为0.2 mM和0.05 mM。Q-6，6-Me2PH2的稳定性有助于确定一种奎宁类二氢蝶呤的化学和物理性质。
The tautomeric structure of the cofactor product of aromatic amino acid hydroxlyases, quinoid dihydrobiopterin, is still unknown. Characterization of this molecule, which is also the substrate for [sheep liver] dihydropteridine reductase has been hindered by the rapid rearrangement of quinoid dihydropterins to 7,8-dihydropterins. This tautomerization can be prevented by disubstitution at the 6-position. A procedure is presented for the synthesis of 6,6-disubstituted pterins from a vicinal diamine and 2-amino-6-chloro-4(3H)-pyrimidinone. The method is illustrated with the specific synthesis of 6,6-dimethyltetrahydropterin (6,6-Me2PH4). 6,6-Me2PH4 is a cofactor for rat liver phenylalanine hydroxylase with enzyme kinetic parameters similar to those of its positional isomer, 6,7-dimethyltetrahydropterin. The resulting quinoid 6,6-dimethyldihydropterin (q-6,6-Me2PH2) is stable; the half-life in 0.1 M Tris-HCl, pH 7.4, at 27 and 37.degree. C is 4 and 1.25 h, respectively. q-6,6-Me2PH2, produced either by phenylalanine hydroxylase or by chemical oxidation of 6,6-Me2PH4, is a substrate for dihydropteridine reductase, with a Km of 0.4 mM and a Vmax double that of the natural isomer of quinoid dihydrobiopterin. In concentrations up to 0.4 mM, q-6,6-Me2PH2 is not an inhibitor of phenylalanine hydroxylase, in contrast to 6-methyl-7,8-dihydropterin and 7,8-dihydrobiopterin which inhibit competitively, with Ki of 0.2 mM and 0.05 mM, respectively. The stability of q-6,6-Me2PH2 has facilitated definitive determination of chemical and physical properties of a quinoid dihydropterin.