STUDIES ON FOLIC ACID AND VITAMIN A

随着甲氨蝶呤(MTX)越来越多地用于治疗关节炎、肝脏 限制这种药物使用的毒性越来越引起人们的关注。因为 二氢叶酸还原酶(DHFR)是该酶的特异性抑制部位。 叶酸拮抗剂，DHFR在肝脏中的功能，特别是在人类 肝脏，是一个重要的研究对象。我们正在继续我们的学习 人肝组织中DHFR的分离和鉴定 和其他物种一样。我们已经发现人类肝脏DHFR的差异 活动取决于组织来源。毫不奇怪，DHFR的活动 在尸检的人肝标本中检测不到。人类 另一方面，在手术中获得的肝脏样本提供了可测量的 用适当的蛋白水解物匀浆时dhfr的活性水平 酶抑制剂。经检测的人体肝脏样本的脱氢表雄酮水平 与鸡肉、牛肉和绵羊的配料相比，Date的价格相当低 肝脏，即牛肉中活性水平的1/100。人肝DHFR， 甲氨蝶呤-琼脂糖亲和层析部分纯化 等电聚焦，有一个摩尔。重量为22,000，等电点为 6.8-7.0。 继续进行研究，以获得更多关于 正常人血浆中类胡萝卜素代谢的高效液相色谱分析 占总类胡萝卜素约10%-15%的峰值与任何已知的 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.