Hall C A, Colligan P D, Begley J A
Nutrition Laboratory for Clinical Assessment and Research, Veterans Administration Medical Center, Albany, New York.
J Cell Physiol. 1987 Oct;133(1):187-91. doi: 10.1002/jcp.1041330125.
The activity of receptors specific for human transcobalamin II-Cobalamin (TC II-Cbl) were measured in virus-transformed lymphoblasts, hepatocytes (hepatoma) and diploid fibro lasts. In all three types of human cells the receptor activity increased as cells went from a resting phase to the most actively dividing phase. Receptor activity declined as cell division slowed. The changes in activity of lymphoblasts and hepatocytes were produced by changes in receptor number and not by changes in affinity between receptors and TC II-Cbl. The basis of the change in fibroblasts was not clear. The Cbl-dependent methionine synthetase activity of fibroblasts, in contrast, tended to be greatest when the cultures were confluent and replication had slowed. As the fibroblasts became senescent the receptor activity for TC II-Cbl declined and the fluctuations with the phase of the cell were blunted. However, the release of apo TC II from the cells was maintained. These observations must be taken into consideration when the respective cells are used as models. Even more important are the implications of the observations of the changes in receptor activity for TC II-Cbl for the regulation of the entry of Cbl into cells.
在病毒转化的淋巴母细胞、肝细胞(肝癌细胞)和二倍体成纤维细胞中检测了人转钴胺素II-钴胺素(TC II-Cbl)特异性受体的活性。在这三种类型的人类细胞中,随着细胞从静止期进入最活跃的分裂期,受体活性均增加。随着细胞分裂减缓,受体活性下降。淋巴母细胞和肝细胞活性的变化是由受体数量的变化引起的,而不是由受体与TC II-Cbl之间亲和力的变化引起的。成纤维细胞变化的基础尚不清楚。相比之下,当成纤维细胞培养物汇合且复制减缓时,其钴胺素依赖性甲硫氨酸合成酶活性往往最高。随着成纤维细胞衰老,TC II-Cbl的受体活性下降,且随细胞周期的波动变得不明显。然而,脱辅基TC II从细胞中的释放得以维持。当将这些细胞用作模型时,必须考虑这些观察结果。更重要的是,关于TC II-Cbl受体活性变化的观察结果对钴胺素进入细胞的调节的影响。