两种蛋氨酸前体的代谢,将L-高半胱氨酸和5'-脱氧-5'-甲硫腺苷与这些化合物在无Met培养基中支持细胞生长的能力进行比较,在以下哺乳动物细胞系中:Raji,CCL39和BHK细胞。这三种细胞系将L-高半胱氨酸和5'-脱氧-5'-甲硫腺苷代谢成甲硫氨酸,S-腺苷-L-甲硫氨酸和蛋白质。然而,代谢和生长研究之间存在差异:Raji细胞可以在L-高半胱氨酸和5'-脱氧-5'-甲硫腺苷上生长,BHK细胞可以在L-高半胱氨酸上生长,但不能在5'-脱氧-5'-甲硫腺苷上生长,CCL39细胞不能在L-高半胱氨酸或5'-脱氧-5'-甲硫腺苷上生长。外源性蛋氨酸的代谢,在CCL39和Raji细胞中研究了由5'-脱氧-5'-甲硫腺苷内源性合成的蛋氨酸,与25microM[甲基-14c]蛋氨酸+25microM5'-脱氧-5'-甲硫腺苷或25microM[甲基-14c]5'-脱氧-5'-甲硫腺苷+25microM蛋氨酸一起孵育:两种细胞中外源和内源蛋氨酸的代谢没有差异。我们的结果表明,i)“甲硫氨酸依赖”最初描述为L-高半胱氨酸[霍夫曼,R.M.和Erbe,R.W.(1976)纳特.Acad.Sci.美国73,1523],也可以观察到与甲硫氨酸的其他前体,即5'-脱氧-5'-甲硫腺苷;ii)“蛋氨酸依赖性”不能被认为是细胞无法在前体内源性合成的蛋氨酸上生长,但取决于所用的前体,而且可能,在不存在蛋氨酸的情况下,前体的毒性作用。
The metabolism of the two methionine precursors, L-homocysteine and 5\'-deoxy-5\'-methylthioadenosine was compared to the ability of these compounds to support cell growth in a Met-free medium, in the following mammalian cell lines: Raji, CCL 39 and BHK cells. These three cell lines metabolized L-homocysteine and 5\'-deoxy-5\'-methylthioadenosine into methionine, S-adenosyl-L-methionine and proteins. However there was a discrepancy between metabolic and growth studies: Raji cells could grow on L-homocysteine and on 5\'-deoxy-5\'-methylthioadenosine, BHK cells could grow on L-homocysteine but not on 5\'-deoxy-5\'-methylthioadenosine, and CCL 39 cells could not grow either on L-homocysteine or on 5\'-deoxy-5\'-methylthioadenosine. The metabolism of exogenous methionine, and of methionine endogenously synthesized from 5\'-deoxy-5\'-methylthioadenosine was studied in CCL 39 and Raji cells, incubated with 25 microM [methyl-14c] methionine + 25 microM 5\'-deoxy-5\'-methylthioadenosine or 25 microM [methyl-14c] 5\'-deoxy-5\'-methylthioadenosine + 25 microM methionine: there was no difference between the metabolism of exogenous and endogenous methionine in either type of cell. Our results indicate that i) \"methionine dependence\" initially described for L-homocysteine [Hoffman, R.M. and Erbe, R.W. (1976) Proc. Natl. Acad. Sci. USA 73, 1523], can also be observed with the other precursor of methionine, ie 5\'-deoxy-5\'-methylthioadenosine; ii) \"methionine-dependence\" can not be considered as the inability of a cell to grow on methionine endogenously synthesized from a precursor, but depends on the precursor used, and possibly, on a toxic effect of the precursor in the absence of methionine.