Iizasa T, Carson D A
Biochim Biophys Acta. 1985 Mar 21;844(3):280-7. doi: 10.1016/0167-4889(85)90128-4.
The consumption of S-adenosylmethionine during polyamine synthesis and transmethylation reactions yields stoichiometric amounts of 5'-deoxy-5'-methylthioadenosine and S-adenosylhomocysteine, respectively. Information concerning the regulation of the two routes of S-adenosylmethionine metabolism in viable cells under changing growth conditions is limited. The present experiments have measured the time-dependent accumulation of 5'-deoxy-5'-methylthioadenosine and L-homocysteine in the medium of four malignant human and murine cell lines deficient in 5'-deoxy-5'-methylthioadenosine phosphorylase (5'-methylthioadenosine: orthophosphate methylthioribosyltransferase). Included in this group were anchorage-independent and anchorage-dependent cells. The enzyme-deficient cells did not detectably cleave 5'-deoxy-5'-methylthioadenosine, and did not appreciably metabolize homocysteine. A comparison of 5'-deoxy-5'-methylthioadenosine and homocysteine excretion therefore provided a noninvasive method for estimating the relative rates of polyamine synthesis and transmethylation. Early after the release of human CEM lymphoblasts from density dependent growth arrest, 5'-deoxy-5'-methylthioadenosine production increased, and exceeded homocysteine synthesis. 5'-Deoxy-5'-methylthioadenosine formation reached a maximum of 0.9 nmol/12 h per 10(6) cells prior to the onset of exponential growth. The kinetics of homocysteine synthesis were different. Homocysteine accumulation was proportional to the specific growth rate, and achieved a peak of 3.1 nmol/12 h per 10(6) cells during mid-exponential phase, at which time 5'-deoxy-5'-methylthioadenosine production was falling. Similar patterns of 5'-deoxy-5'-methylthioadenosine and homocysteine excretion were observed in other 5'-deoxy-5'-methylthioadenosine phosphorylase deficient cell lines. These data show that polyamine synthesis and transmethylation are differentially regulated during the growth cycle of mammalian cells.
在多胺合成和转甲基反应过程中，S-腺苷甲硫氨酸的消耗分别产生化学计量的5'-脱氧-5'-甲硫基腺苷和S-腺苷高半胱氨酸。关于在变化的生长条件下活细胞中S-腺苷甲硫氨酸代谢的两条途径的调控信息有限。本实验测量了四种缺乏5'-脱氧-5'-甲硫基腺苷磷酸化酶（5'-甲硫基腺苷：正磷酸甲基硫代核糖基转移酶）的人类和小鼠恶性细胞系培养基中5'-脱氧-5'-甲硫基腺苷和L-高半胱氨酸随时间的积累。该组包括不依赖贴壁和依赖贴壁的细胞。酶缺陷细胞无法检测到5'-脱氧-5'-甲硫基腺苷的裂解，也无法明显代谢高半胱氨酸。因此，比较5'-脱氧-5'-甲硫基腺苷和高半胱氨酸的排泄提供了一种非侵入性方法来估计多胺合成和转甲基的相对速率。人类CEM淋巴母细胞从密度依赖性生长停滞中释放后不久，5'-脱氧-5'-甲硫基腺苷的产生增加，并超过了高半胱氨酸的合成。在指数生长开始之前，5'-脱氧-5'-甲硫基腺苷的形成达到每10(6)个细胞0.9 nmol/12 h的最大值。高半胱氨酸合成的动力学不同。高半胱氨酸的积累与比生长速率成正比，并在指数中期达到每10(6)个细胞3.1 nmol/12 h的峰值，此时5'-脱氧-5'-甲硫基腺苷的产生正在下降。在其他5'-脱氧-5'-甲硫基腺苷磷酸化酶缺陷细胞系中也观察到了类似的5'-脱氧-5'-甲硫基腺苷和高半胱氨酸排泄模式。这些数据表明，在哺乳动物细胞的生长周期中，多胺合成和转甲基受到不同的调控。
