The crystal and molecular structure of folic acid dihydrate has been determined by x-ray diffraction. Folic acid is in an extended conformation with the pteridine ring in the keto form. The C(4) oxygen and N(10) atoms are on the same side of the molecule, hydrogen-bonded to the same water. This conformation has the pteridine rotated approximately 180 degrees away from the orientation of the pteridine ring of methotrexate bound to dihydrofolate reductase. The folic acid pteridine and phenyl rings interact in a stacking manner which is suggestive of the type of associations these groups could form in a complex of folate, dihydrofolate reductase, and reduced nicotinamide adenine dinucleotide phosphate.

中文翻译：

---

叶酸：晶体结构和对酶结合的影响

叶酸二水合物的晶体和分子结构已通过 X 射线衍射确定。叶酸与酮形式的蝶啶环呈扩展构象。C(4) 氧和 N(10) 原子位于分子的同一侧，氢键连接到同一水。这种构象使蝶啶从与二氢叶酸还原酶结合的甲氨蝶呤蝶啶环的方向旋转大约 180 度。叶酸蝶啶和苯环以堆叠方式相互作用，这表明这些基团可以在叶酸、二氢叶酸还原酶和还原型烟酰胺腺嘌呤二核苷酸磷酸的复合物中形成的缔合类型。