German D C, Bloch C A, Kredich N M
J Biol Chem. 1983 Sep 25;258(18):10997-1003.
The intracellular content and turnover of S-adenosyl-L-methionine (AdoMet) were measured in cultured human lymphoid cells. AdoMet levels were found to be 59 nmol/ml cell volume in exponentially growing WI-L2 lymphoblasts, 3.3-8.1 nmol/ml cell volume in unstimulated peripheral blood mononuclear cells, and 25-33 nmol/ml cell volume 24-48 h after the latter were stimulated with phytohemagglutinin. Increases in the AdoMet content of stimulated cells occurred within 2 h after addition of lectin. First order, pool turnover rates were of the same order of magnitude (0.029-0.091/min) for all three types of cultured cells, but owing to the differences in AdoMet content, absolute utilization rates differed markedly and were 4.5, 0.12-0.40, and 1.41-1.57 nmol/min/ml cell volume in WI-L2, unstimulated peripheral mononuclear cells, and lectin-stimulated peripheral mononuclear cells, respectively. Measurements of homocysteine accumulation in growth medium and of transsulfuration to cysteine indicate that a minimum of 82% of the AdoMet synthesized by WI-L2 is used for transmethylation. Remethylation of homocysteine by these cells could not be detected. AdoMet synthesis accounts for 20-23% of methionine utilization by WI-L2. Judging from the accumulation of homocysteine in the medium of phytohemagglutinin-stimulated peripheral mononuclear cells, a minimum of 38% of AdoMet synthesized must be used for transmethylation. Even though AdoMet utilization by unstimulated peripheral mononuclear cells is relatively small compared to that of stimulated cells and WI-L2, our data indicate that AdoMet turnover in such "resting" cells is three to five times that estimated for nonhepatic tissues. These findings may be relevant to the hypothesis that lymphoid cells are unusually sensitive to inhibition of transmethylation reactions.
在培养的人淋巴细胞中测量了S-腺苷-L-甲硫氨酸（AdoMet）的细胞内含量和周转率。发现在指数生长的WI-L2淋巴母细胞中，AdoMet水平为59 nmol/ml细胞体积；在未刺激的外周血单核细胞中为3.3 - 8.1 nmol/ml细胞体积；在用植物血凝素刺激后24 - 48小时，外周血单核细胞中的AdoMet水平为25 - 33 nmol/ml细胞体积。添加凝集素后2小时内，受刺激细胞的AdoMet含量增加。对于所有三种类型的培养细胞，一级池周转率处于相同数量级（0.029 - 0.091/分钟），但由于AdoMet含量不同，绝对利用率差异显著，在WI-L2、未刺激的外周单核细胞和凝集素刺激的外周单核细胞中分别为4.5、0.12 - 0.40和1.41 - 1.57 nmol/分钟/毫升细胞体积。对生长培养基中同型半胱氨酸积累以及向半胱氨酸的转硫作用的测量表明，WI-L2合成的AdoMet至少82%用于甲基转移。未检测到这些细胞对同型半胱氨酸的再甲基化作用。AdoMet合成占WI-L2甲硫氨酸利用率的20 - 23%。从植物血凝素刺激的外周血单核细胞培养基中同型半胱氨酸的积累判断，合成的AdoMet至少38%必须用于甲基转移。尽管与受刺激细胞和WI-L2相比，未刺激的外周血单核细胞对AdoMet的利用率相对较小，但我们的数据表明，此类“静止”细胞中AdoMet的周转率是非肝组织估计值的三到五倍。这些发现可能与淋巴细胞对甲基转移反应抑制异常敏感的假说相关。
