Flintoff W F, Nagainis C R
Arch Biochem Biophys. 1983 Jun;223(2):433-40. doi: 10.1016/0003-9861(83)90607-0.
The uptake of several folate compounds has been investigated in wild-type and one class of methotrexate-resistant Chinese hamster ovary cells. The wild-type cells can take up methotrexate, folic acid, and 5-methyl tetrahydrofolate. The uptake of methotrexate is characterized by a KT of 1.9 +/- 0.2 microM and a Vmax of 1 +/- 0.8 pmol/min/mg protein, is competitively inhibited by folic acid and 5-methyl tetrahydrofolate, and is sensitive to p-hydroxymercuriphenyl sulfonic acid. The resistant cells are unable to take up methotrexate, folic acid, and 5-methyl tetrahydrofolate. In addition, the resistant cells are unable to bind methotrexate specifically, whereas the wild-type cells bind the drug with an apparent KD of 2 +/- 0.4 microM and a Vmax of 1.3 +/- 0.3 pmol/mg protein. These data indicate that the resistant cells are resistant because of an inability to take up the drug resulting from a defective membrane-binding component. The data also suggest that both methotrexate and folic acid are transported by the same system in Chinese hamster ovary cells.
已对野生型和一类对甲氨蝶呤耐药的中国仓鼠卵巢细胞摄取几种叶酸化合物的情况进行了研究。野生型细胞能够摄取甲氨蝶呤、叶酸和5-甲基四氢叶酸。甲氨蝶呤的摄取特点为转运常数（KT）为1.9±0.2微摩尔，最大转运速率（Vmax）为1±0.8皮摩尔/分钟/毫克蛋白质，受叶酸和5-甲基四氢叶酸竞争性抑制，且对对羟基汞苯磺酸敏感。耐药细胞无法摄取甲氨蝶呤、叶酸和5-甲基四氢叶酸。此外，耐药细胞无法特异性结合甲氨蝶呤，而野生型细胞结合该药物的表观解离常数（KD）为2±0.4微摩尔，最大结合速率（Vmax）为1.3±0.3皮摩尔/毫克蛋白质。这些数据表明，耐药细胞产生耐药性是由于膜结合成分存在缺陷而无法摄取药物。数据还表明，在中国仓鼠卵巢细胞中，甲氨蝶呤和叶酸由同一系统转运。
