Jargiello P
Biochim Biophys Acta. 1982 Jul 30;698(1):78-85. doi: 10.1016/0167-4781(82)90187-7.
Ribokinase, the first enzyme in ribose catabolism, is altered in its expression in ribose-utilizing Novikoff hepatoma variants. 90% of the variants selected for their ability to use D-ribose as a sole carbon source show a change in ribokinase activity. After non-selective growth, phenotypically unstable variants lose their altered expression and regain a parental form of expression of this enzyme. In the variants, ribokinase expression in non-inducible by the carbon source and is unaffected by the growth phase of the cells. However, ribokinase expression in both parental cells and variants is cell cycle-dependent. Parental Novikoff hepatoma cells have three peaks of ribokinase activity during the S, G2 and M phases. Variants are described which have high basal levels of ribokinase and only a single peak of enzymatic activity during the S phase. In addition to changes in the level of ribokinase, changes in the subcellular localization of the enzyme have been found in some variants. While the change in the level of ribokinase seems to be a property of the variant isolated, the change in subcellular location of ribokinase can be readily achieved by culture conditions.
核糖激酶是核糖分解代谢中的第一种酶，在利用核糖的诺维科夫肝癌变种中，其表达发生了改变。90%因能够将D-核糖作为唯一碳源而被筛选出的变种，其核糖激酶活性发生了变化。在非选择性生长后，表型不稳定的变种会失去其改变后的表达，重新恢复该酶的亲本表达形式。在这些变种中，核糖激酶的表达不受碳源诱导，也不受细胞生长阶段的影响。然而，亲本细胞和变种中的核糖激酶表达均依赖于细胞周期。亲本诺维科夫肝癌细胞在S期、G2期和M期有三个核糖激酶活性峰值。已描述的变种具有高基础水平的核糖激酶，且在S期只有一个酶活性峰值。除了核糖激酶水平的变化外，在一些变种中还发现了该酶亚细胞定位的变化。虽然核糖激酶水平的变化似乎是所分离变种的一个特性，但核糖激酶亚细胞定位的变化可以通过培养条件轻易实现。
