Purine and pyrimidine transport and phosphoribosylation and their interaction in overall uptake by cultured mammalian cells. A re-evaluation.
Purine and pyrimidine transport and phosphoribosylation and their interaction in overall uptake by cultured mammalian cells. A re-evaluation.
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嘌呤和嘧啶转运和磷酸核糖基化及其在培养的哺乳动物细胞总体摄取中的相互作用。
DOI：
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发表时间：
1979
影响因子：
4.8
通讯作者：
P. Plagemann
中科院分区：
文献类型：
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作者：
R. Marz;R. Wohlhueter;P. Plagemann
在Novikoff大鼠肝癌、小鼠L、P388小鼠白血病和中国仓鼠卵巢细胞的悬浮液中，通过快速动力学技术测量嘌呤和嘧啶的零反式摄取，该技术允许以短至1.5 s的间隔测定摄取时间点。嘌呤/嘧啶转运的动力学参数通过测量进入细胞的底物内流来确定，其中由于缺乏适当的酶或由于ATP（5 '-磷酸核糖焦磷酸）的细胞消耗，底物转化为核苷酸可以忽略不计，并且通过计算机拟合针对各种载体介导的转运模型直接导出的精确的积分速率方程来确定零反式内流数据。结果表明，不同的载体在次黄嘌呤/鸟嘌呤，腺嘌呤和尿嘧啶的运输中起作用，对于Novikoff细胞，在24 ℃下，与底物：载体缔合常数（K）分别为300至400 μ M，2至3 mM和约14 mM。L和P388细胞转运次黄嘌呤的K和Vmax与Novikoff细胞相似，但中国仓鼠卵巢细胞的转运能力低得多，K = 1500 μ M。所有的交通系统都是完全对称的。次黄嘌呤转运如此之快，以至于在24 ℃下孵育20至50 s内，至少在低于K的细胞外浓度下，游离次黄嘌呤的细胞内浓度（90%）接近培养基中的浓度。在转化为核苷酸未被阻断的细胞中，游离次黄嘌呤以相同的速度在细胞内积累到稳态水平，此后次黄嘌呤摄取到总细胞物质中的速率严格地是磷酸核糖基化速率的函数。以前在许多类型的细胞中检测到的次黄嘌呤（1至9 μ M）和腺嘌呤（0.2至40 μ M）摄取的低Km系统反映了相应的磷酸核糖基转移酶的底物饱和度，而不是运输系统。
The zero-trans uptake of purines and pyrimidines was measured in suspensions of Novikoff rat hepatoma, mouse L, P388 mouse leukemia, and Chinese hamster ovary cells by a rapid kinetic technique which allows the determination of uptake time points in intervals as short as 1.5 s. Kinetic parameters for purine/pyrimidine transport were determined by measuring substrate influx into cells in which substrate conversion to nucleotides was negligible either due to lack of the appropriate enzymes or to depletion of the cells of ATP (5'-phosphoribosylpyrophosphate), and by computer fitting exact, integrated rate equations derived for various carrier-mediated transport models directly to zero-trans influx data. The results indicate that different carriers function in the transport of hypoxanthine/guanine, adenine, and uracil with substrate:carrier association constants (K) at 24 degrees C of 300 to 400 muM, 2 to 3 mM, and about 14 mM, respectively, for Novikoff cells. K and Vmax for hypoxanthine transport by L and P388 cells are similar to those for Novikoff cells, but the transport capacity of Chinese hamster ovary cells is much lower and K = 1500 muM. All transport systems are completely symmetrical. Hypoxanthine transport is so rapid that an intracellular concentration of free hypoxanthine (90%) close to that in the medium is attained within 20 to 50 s of incubation at 24 degrees C, at least at extracellular concentrations below K. In cells in which conversion to nucleotides is not blocked free hypoxanthine accumulates intracellularly to steady state levels with equal rapidity and thereafter the rate of hypoxanthine uptake into total cell material is strictly a function of the rate of phosphoribosylation. The low Km systems for hypoxanthine (1 to 9 muM) and adenine (0.2 to 40 muM) uptake detected previously in many types of cells reflect the substrate saturation of the respective phosphoribosyltransferases rather than of the transport system.