STUDIES ON FOLIC ACID AND VITAMIN A

叶酸辅助因子以聚谷氨酸形式存在于细胞内 衍生品。发现某些抗叶酸药物是 转化为类似的多谷氨酸增加了一种 这类衍生物在化疗中的作用。 利用从不同来源分离的二氢叶酸还原酶(DHFR) 动物肝脏对DHFR抑制作用的某些比较方面 药物甲氨蝶呤(MTX)的聚谷氨酰胺衍生物和10- 去氮氨基蝶呤(10-DAM)与强效的比较 相应的单谷氨酸盐的抑制性能是 调查过了。对绵羊的影响最显著 肝脏DHFR。MTX的多谷氨酰化导致逐步增加 在抑制中。六个谷氨酸残基的抑制力比 单谷氨酸盐。增加10-DAM上的Glu链将减少 链长达3的抑制作用。进一步增加 现在导致了越来越多的抑制作用。反应的动力学参数 谷氨酸二氢蝶酰酯和谷氨酸二氢蝶酰酯 (二氢叶酸)在这项研究中似乎是相同的。然而， 当使用五氨基谷氨酸作为底物时， 二氢叶酸的抑制程度也相应 MTX和10-DAM都减少了2到5倍 五谷氨酸衍生物。 正常人血浆中类胡萝卜素的含量 在标准化条件下是高度可变的，而所有 摄入纯β-胡萝卜素的受试者在 大约30小时后，这些反应的幅度至少相差3倍。 当作为纯化合物喂养时，β-胡萝卜素与 煮熟的胡萝卜也有同样的剂量。等离子体响应的研究 不同的膳食类胡萝卜素来源显示，血浆 类胡萝卜素浓度不能准确反映饮食摄入量 某些促维生素，如叶黄素、番茄红素等。

Folate cofactors exist intracellularly as polyglutamate derivatives. The discovery that certain antifolate drugs are converted to similar polyglutamates has raised the possibility of a role for such derivates in chemotherapy. Using dihydrofolate reductases (DHFR) isolated from various animal livers certain comparative aspects of DHFR inhibition by polyglutamyl derivates of the drugs methotrexate (MTX) and 10- deazaaminopterin (10-DAM) as compared with the potent inhibitory properties of the corresponding monoglutamates were investigated. The most striking effects were seen with sheep liver DHFR. Polyglutamylation of MTX causes stepwise increases in inhibition. Six Glu residues is 3-X more inhibitory than the monoglutamate. Increasing the Glu chain on 10-DAM decreases the inhibitory effects up to a chain length of 3. Further increases now result in increasing inhibition. The kinetic parameters of dihydropteroyl-perntaglutamate and dihyropteroylglutamate (dihydrofolate) appear to be identical in this study. However, when the pentafglutamate is used as substrate instead of dihydrofolate, the degree of inhibition is correspondingly decreased 2- to 5- fold for both the MTX and 10-DAM pentaglutamate derivatives. The amount of carotenoids appearing in the plasma of normal men under standardized conditions is highly variable, whereas all subjects ingesting pure beta-carotene gave maximum responses in about 30 hr, the magnitude of the responses varied at least 3-fold. Beta -carotene when fed as the pure compound was comparable to the same dose from cooked carrots. Study of the plasma response to different dietary carotenoid sources revealed that plasma carotenoid concentrations do not accurately reflect dietary intake of certain pro-vitamins, ie., lutein, lycopene, etc.