Cohen E A, Filion M, Suh M, Langelier Y
Biochem Cell Biol. 1987 Jan;65(1):35-42. doi: 10.1139/o87-005.
Ribonucleotide reductase from mammalian cells is composed of two nonidentical subunits M1 and M2 which are both required to form the catalytic site. The level of ribonucleotide reductase activity is cell cycle controlled and several reports suggest that this control is achieved mainly by the regulation of M2 subunit synthesis. In the present study, we have found that the activities of both subunits decreased markedly upon serum starvation in the Syrian baby hamster kidney 21/C13 cell line. These decreases did not seem to be correlated with the appearance of an inhibitory factor in serum-starved cells. Quantification of the amount of the M1 subunit protein (89,000 molecular weight) by [32P]dTTP photoaffinity labelling revealed that the decrease in M1 activity was not due to variation in M1 protein level. Therefore, a posttranslational mechanism probably exists which inactivates M1 subunit when cells stay in the quiescent (G0) state and this mechanism could play an important role in the control of ribonucleotide reductase activity.
哺乳动物细胞中的核糖核苷酸还原酶由两个不同的亚基M1和M2组成，这两个亚基都是形成催化位点所必需的。核糖核苷酸还原酶的活性水平受细胞周期调控，有几份报告表明，这种调控主要是通过对M2亚基合成的调节来实现的。在本研究中，我们发现，在叙利亚仓鼠肾21/C13细胞系中，血清饥饿后两个亚基的活性均显著降低。这些降低似乎与血清饥饿细胞中抑制因子的出现无关。通过[32P]dTTP光亲和标记对M1亚基蛋白（分子量89,000）的量进行定量分析表明，M1活性的降低并非由于M1蛋白水平的变化。因此，可能存在一种翻译后机制，当细胞处于静止（G0）状态时使M1亚基失活，并且这种机制可能在核糖核苷酸还原酶活性的调控中起重要作用。
