Koren R, Shohami E, Yeroushalmi S
Eur J Biochem. 1979 Apr 2;95(2):333-9. doi: 10.1111/j.1432-1033.1979.tb12970.x.
We present here a differentiation by kinetic methods of the tandem processes of transport and metabolic during uptake of cytosine-beta-D-arabinoside by intact rat fibroblasts. Transport across the cell membrane occurs by a carrier-mediated mechanism displaying a Km of approximately 500 microM and a V of approximately pmol x min-1 x (10(6) cells)-1. The subsequent metabolic trapping (phosphorylation) has a Km of approximately 15 microM and V of approximately 0.25 pmol x min-1 x (10(6) cells)-1. In this system, transport is rate-limiting for the first phase of the uptake process whereas phosphorylation becomes rate-limiting when internal concentration of radioactive labeled substrate exceeds that in the extracellular medium. The duration of the first phase depends on the substrate concentration.
我们在此展示通过动力学方法对完整大鼠成纤维细胞摄取胞嘧啶-β-D-阿拉伯糖苷过程中转运和代谢串联过程的区分。跨细胞膜的转运通过载体介导机制发生，其Km约为500微摩尔，V约为皮摩尔×分钟⁻¹×(10⁶个细胞)⁻¹。随后的代谢捕获（磷酸化）Km约为15微摩尔，V约为0.25皮摩尔×分钟⁻¹×(10⁶个细胞)⁻¹。在该系统中，转运是摄取过程第一阶段的限速步骤，而当放射性标记底物的细胞内浓度超过细胞外培养基中的浓度时，磷酸化成为限速步骤。第一阶段的持续时间取决于底物浓度。
