Hall C A
J Lab Clin Med. 1984 Jan;103(1):70-81.
The phase of the cell cycle permitting transcobalamin II (TC II) mediated entry of cobalamin (Cbl) into human lymphocytes was determined under several conditions. (1) Little was taken up by resting peripheral blood lymphocytes (PBL). (2) Uptake was enhanced by stimulation of PBL by culture with a mitogen. (3) This increase in capacity for uptake took place simultaneously during 3 days of culture with the increase in capacity to synthesize DNA. (4) Hydroxyurea inhibited both DNA synthesis and TC II-Cbl uptake. (5) As culture was prolonged and the cells passed beyond the phase of most active division, DNA synthesis and Cbl uptake declined sharply. (6) The increased capacity to take up Cbl after stimulation was determined, at least in part, by increased receptor activity for TC II-Cbl. (7) Internalization of the Cbl was also increased. (8) Simultaneously with the increasing DNA synthesis, the cells increased in the activity of the Cbl-dependent methionine synthetase (MS). (9) MS activity subsequently fell during longer culture. Thus PBL can take in Cbl only during a narrow "window" in the cell cycle. This window is associated with the period of most active DNA synthesis and at a time when one coenzyme of Cbl, MeCbl, is the most active.
在多种条件下，确定了细胞周期中允许转钴胺素II（TC II）介导钴胺素（Cbl）进入人淋巴细胞的阶段。（1）静息外周血淋巴细胞（PBL）摄取的Cbl很少。（2）用促有丝分裂原培养刺激PBL可增强摄取。（3）在培养3天期间，摄取能力的这种增加与DNA合成能力的增加同时发生。（4）羟基脲抑制DNA合成和TC II-Cbl摄取。（5）随着培养时间延长，细胞越过最活跃分裂阶段，DNA合成和Cbl摄取急剧下降。（6）刺激后摄取Cbl能力的增加至少部分是由TC II-Cbl受体活性增加所致。（7）Cbl的内化也增加。（8）随着DNA合成增加，细胞中钴胺素依赖性甲硫氨酸合成酶（MS）的活性也增加。（9）在更长时间的培养过程中，MS活性随后下降。因此，PBL仅在细胞周期的一个狭窄“窗口”期间摄取Cbl。这个窗口与最活跃的DNA合成期相关，且此时Cbl的一种辅酶，甲基钴胺素（MeCbl）最为活跃。
