HIGH INVIVO RATES OF METHIONINE BIOSYNTHESIS IN TRANSFORMED HUMAN AND MALIGNANT RAT CELLS AUXOTROPHIC FOR METHIONINE
HIGH INVIVO RATES OF METHIONINE BIOSYNTHESIS IN TRANSFORMED HUMAN AND MALIGNANT RAT CELLS AUXOTROPHIC FOR METHIONINE
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DOI：
10.1073/pnas.73.5.1523
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发表时间：
1976-01-01
影响因子：
11.1
通讯作者：
ERBE, RW
中科院分区：
文献类型：
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作者：
HOFFMAN, RM;ERBE, RW
与正常细胞不同，恶性大鼠和2 SV 40转化的人细胞系既不能生长，也不能在B12和叶酸补充的培养基中生存，其中蛋氨酸被同型半胱氨酸取代。然而，3条证据表明，恶性和转化细胞通过5-甲基四氢蝶酰-L-谷氨酸：L-同型半胱氨酸S-甲基转移酶（EC-2.1.1.13）催化的反应内源性合成大量蛋氨酸。这种甲基转移酶的活性在恶性和正常细胞的提取物中相当。从[5- 14 C]甲基四氢蝶酰-L-谷氨酸（5-Me-H4 PteGlu）摄取放射性标记在恶性细胞中至少与正常细胞中一样大，并且几乎完全依赖于添加高半胱氨酸（甲基受体）; 59-84%的细胞掺入的标记以甲硫氨酸形式回收。恶性和转化的细胞不能单独在同型半胱氨酸中生长，而在存在其他限制性抗体的情况下，如果外源性蛋氨酸，同型半胱氨酸刺激这些细胞的生长。启动正常和恶性和转化细胞生长所需的蛋氨酸的最低浓度在所有细胞系中是相同的，并且在最佳蛋氨酸浓度下的最大生长速率不能区分正常细胞和恶性和转化细胞。内源性合成的甲硫氨酸很容易被恶性和转化细胞纳入高分子量物质中，表明在利用中没有普遍的缺陷。高密度接种不允许这些细胞在蛋氨酸缺乏培养基中的同型半胱氨酸上生长，也不忽略7种非必需氨基酸影响生长，这表明对外源性蛋氨酸的依赖不是由于蛋氨酸单独或与其他氨基酸一起泄漏。尽管存在高水平的内源性合成，但生长对外源性甲硫氨酸的需求目前尚不清楚，但似乎可以将某些致癌转化但在其他方面差异很大的细胞系与正常细胞区分开来。
Unlike normal cells, malignant rat and 2 SV 40-transformed human cell lines can neither grow nor survive in B12- and folate-supplemented media in which methionine is replaced by homocysteine. Yet 3 lines of evidence indicate that the malignant and transformed cells synthesize large amounts of methionine endogenously through the reaction catalyzed by 5-methyltetrahydropteroyl-L-glutamate: L-homocysteine S-methyltransferase (EC-2.1.1.13). The activities of this methyltransferase were comparable in extracts of malignant and normal cells. The uptake of radioactive label from [5-14C]methyltetrahydropteroyl-L-glutamic acid (5-Me-H4PteGlu) was at least as great in the malignant cells as in the normals and was nearly totally dependent on the addition of homocysteine, the methyl acceptor; 59-84% of the label incorporated by cells was recovered as methionine. The malignant and transformed cells were unable to grow in homocysteine alone, while in the presence of otherwise limiting aniybts if exogenous methionine, homocysteine stimulated the growth of these cells. The minimum concentration of methionine necessary to initiate growth of normal and malignant and transformed cells was the same in all lines, and the maximal growth rates at optimal methionine concentrations did not distinguish the normal from the malignant and transformed cells. The endogenously synthesized methionine was readily incorporated into high MW substances by malignant and transformed cells, indicating the absence of a generalized defect in utilization. Inoculation at high density did not allow these cells to grow on homocysteine in methionine deficient media nor did the omission of the 7 nonessential amino acids affect growth, suggesting that the dependence on exogenous methionine is not due to leakage of methionine alone or with other amino acids. The requirement for exogenous methionine for growth, despite high levels of endogenous synthesis, is presently unexplained but appears to distinguish certain oncogenically transformed, but otherwise widely varying, cell lines from normals.