the alpha-carboxyl of folyl monoglutamates would allow correct positioning of the terminal gamma-carboxyl of the chain for reaction. This binding mechanism would be compatible with the utilization of a single enzyme species for the addition of glutamate to the monoglutamate or oligoglutamate forms of folates and folate analogues.
已经研究了α-羧基在
甲氨蝶呤(MeAPA-Glu)和
甲氨蝶呤的γ-谷
氨酸衍
生物(MeAPA-Glu-Glu)在叶酰聚谷
氨酸合成酶(F
PGS)催化的反应中的作用。小鼠肝蛋白的(NH4)2SO4沉淀物中所含的F
PGS种类相同的F
PGS物质将MeAPA-Glu和MeAPA-Glu-Glu接受为底物,可以通过在两种底物的饱和浓度下缺乏产品形成的加性来判断。MeAPA-Gaba,一种缺乏α-羧基的MeAPA-Glu类似物,没有活性作为该酶的底物,MeAPA-Glu-Gaba,即缺乏末端谷
氨酸的α-羧基的MeAPA-Glu-Glu的类似物。但是,MeAPA-Gaba-Glu是MeAPA-Glu-Glu的类似物,在第一个谷
氨酸上没有α-羧基,F
PGS的底物活性接近MeAPA-Glu-Glu。这些结果表明,α-羧基对于叶酰单谷
氨酸以正确的取向结合至F
PGS以进行催化是必不可少的。此外,叶酰低聚谷
氨酸酯的末