STUDIES ON FOLIC ACID AND VITAMIN A

随着越来越多地使用甲氨蝶呤（MTX）治疗关节炎，肝脏 限制这种药物使用的毒性越来越受到关注。 因为 二氢叶酸还原酶（DHFR）是抑制这种酶的特异性位点。 叶酸拮抗剂，DHFR在肝脏中的功能，特别是人 肝脏是一个重要的研究对象。 我们继续我们的研究 从人类肝脏样品中分离和表征肝脏DHFR， 和其他物种一样。 我们发现人类肝脏DHFR 活性取决于组织来源。 毫不奇怪，DHFR活性 在尸体解剖的人类肝脏标本中无法检测到。 人类 另一方面，手术期间获得的肝脏样本提供了可测量的 DHFR活性水平，当用适当的蛋白水解 酶抑制剂 检测的人肝脏样本的DHFR水平， 与鸡肉、牛肉和羊肉相比， 肝脏，即牛肉活性水平的1/100。 人肝DHFR， 通过在MTX-琼脂糖凝胶上的亲和色谱法部分纯化， 等电聚焦，具有摩尔比。重量22，000的等电点为 6.8-7.0. 继续进行研究， 正常人的类胡萝卜素代谢：人血浆的HPLC分析给出了 总类胡萝卜素的10 - 15%的峰值不同于任何已知的 标准化合物。 目前的研究表明，这种未知化合物可能 是羟基-α-胡萝卜素。

With the increasing use of methotrexate (MTX) to treat arthritis, liver toxicity, which limits use of this drug, is of increasing concern. Because dihydrofolate reductase (DHFR) is the specific site of inhibition of this folic acid antagonist, the function of DHFR in liver, particularly human liver, is an important research objective. We are continuing our studies to isolate and characterize hepatic DHFR from human liver samples as well as from other species. We have found differences in human liver DHFR activity depending upon the tissue source. Not surprisingly, DHFR activity could not be detected in preparations of human liver from autopsies. Human liver samples obtained during surgery, on the other hand, gave measurable levels of DHFR activity when homogenized with appropriate proteolytic enzyme inhibitors. The DHFR levels of the human liver samples tested to date are quite low compared to preparations of chicken, beef, and sheep liver, i.e. 1/100 the level of activity in beef. Human hepatic DHFR, partially purified by affinity chromatography on MTX-sepharose followed by isoelectric focusing, has a mol. wt. of 22,000 and an isoelectric point of 6.8-7.0. Continuation of the studies to obtain more detailed information on carotenoid metabolism in normal humans: HPLC analysis of human plasma gave a peak of some 10-15% of total carotenoids different from any known standard compounds. Current studies suggest that the unknown compound may be hydroxy-alpha-carotene.