Kramer D L, Sufrin J R, Porter C W
Grace Cancer Drug Center, Roswell Park Memorial Institute, Buffalo, NY 14263.
Biochem J. 1987 Oct 15;247(2):259-65. doi: 10.1042/bj2470259.
Treatment of cultured L1210 cells with 1 mM-L-2-amino-4-methoxy-cis-but-3-enoic acid (L-cisAMB), a methionine-analogue inhibitor of S-adenosylmethionine (AdoMet) synthetase (EC 2.5.1.6), produced a rapid and near-total depletion of AdoMet by 4 h. After this, the pools recovered to 60% of control by 48 h, apparently because of an increase in AdoMet synthetase activity. Both AdoMet depletion and the accompanying increase in synthetase activity were substantially enhanced by lowering methionine concentrations in the media from 100 microM to 30 microM, the minimal concentration that supports cell growth at control values. During a 4 h incubation in media containing 30 microM-methionine, 1-5 mM-L-cisAMB depleted cellular AdoMet to undetectable values, and inhibited nucleic acid methylation by 44-72% and RNA methylation by 60-87%. Under these same treatment conditions, putrescine pools increased by about 3-fold, whereas spermidine pools decreased by only 20% and spermine pools remained the same. Pool changes were accompanied by a 2-4-fold increase in ornithine decarboxylase activities and AdoMet activities. Thus the rapid depletion of AdoMet pools by L-cisAMB results immediately in a decrease in methyl-transfer reactions involving nucleic acids, whereas, by contrast, biosynthesis of higher polyamines appears to be minimally affected, owing to compensatory increases in key enzyme activities.
用1 mM - L - 2 - 氨基 - 4 - 甲氧基 - 顺式 - 丁 - 3 - 烯酸（L - 顺式AMB）处理培养的L1210细胞，L - 顺式AMB是S - 腺苷甲硫氨酸（AdoMet）合成酶（EC 2.5.1.6）的甲硫氨酸类似物抑制剂，4小时内可使AdoMet迅速且几乎完全耗尽。此后，到48小时时，其水平恢复到对照值的60%，这显然是由于AdoMet合成酶活性增加所致。将培养基中甲硫氨酸浓度从100 microM降至30 microM（这是在对照值下支持细胞生长的最低浓度），可显著增强AdoMet的耗尽以及合成酶活性的伴随增加。在含有30 microM甲硫氨酸的培养基中孵育4小时期间，1 - 5 mM - L - 顺式AMB将细胞内的AdoMet耗尽至检测不到的值，并使核酸甲基化受到44 - 72%的抑制，RNA甲基化受到60 - 87%的抑制。在相同的处理条件下，腐胺水平增加约3倍，而亚精胺水平仅下降20%，精胺水平保持不变。这些水平变化伴随着鸟氨酸脱羧酶活性和AdoMet活性增加2 - 4倍。因此，L - 顺式AMB使AdoMet水平迅速耗尽，立即导致涉及核酸的甲基转移反应减少，而相比之下，由于关键酶活性的代偿性增加，高级多胺的生物合成似乎受到的影响最小。
