Givas J K, Gutcho S
Clin Chem. 1975 Mar;21(3):427-8.
We compare the binding of folic acid and N-5-methyltetrahydrofolic acid to milk binder in the pH range 7.4 to 10.1. At pH 7.4 the relative affinities are quite disparate, with folic acid showing the greater affinity for milk binder. As the pH is increased from 7.4 to 9.3, the difference in affinities becomes smaller, and at pH 9.3 the affinities are nearly the same. As the pH is increased from 9.3 to 10.1, the relative affinities again begin to differ, with N-5-methyltetrahydrofolic acid displaying the greater affinity. These results indicate that at a pH of 9.3 the more stable folic acid may be used as the standard in radioassay of endogenous folates.
我们比较了叶酸和N-5-甲基四氢叶酸在pH值7.4至10.1范围内与乳结合剂的结合情况。在pH 7.4时，相对亲和力差异很大，叶酸对乳结合剂表现出更高的亲和力。随着pH值从7.4增加到9.3，亲和力差异变小，在pH 9.3时亲和力几乎相同。随着pH值从9.3增加到10.1，相对亲和力再次开始不同，N-5-甲基四氢叶酸表现出更高的亲和力。这些结果表明，在pH 9.3时，更稳定的叶酸可作为内源性叶酸放射测定的标准。
