Plagemann P G, Wohlhueter R M, Erbe J
J Biol Chem. 1982 Oct 25;257(20):12069-74.
Rapid kinetic techniques were employed to measure the transport of uridine and thymidine in human erythrocytes in zero-trans entry and exist and equilibrium exchange procedures. The kinetic parameters of transport were computed by fitting appropriate integrated rate equations to time courses of transmembrane equilibration of radiolabeled substrate. Transport of uridine and thymidine conformed to the simple carrier model with directional symmetry, but differential mobility of loaded and empty carrier. As was apparent from comparison of zero-trans influx and equilibrium exchange flux, the loaded carrier moved 3 to 18 times faster than the empty carrier in batches of erythrocytes obtained from different individuals. The maximum equilibrium exchange velocities also differed for different batches of erythrocytes. Storage of the cells at 4 degrees C for 4 days or treatment of cells with oxidizing or reducing agents or suspension in hypotonic solutions had no effect on the kinetic properties of the nucleoside transporter. All natural ribo- and deoxyribonucleosides tested when present on the trans side at concentrations well above the Michaelis-Menten constant for transport accelerated the influx and efflux of uridine and inhibited uridine influx when present at these concentrations on the cis side, but nucleobases had no significant effect.
采用快速动力学技术，在零转运进入、流出及平衡交换过程中测量人红细胞中尿苷和胸苷的转运。通过将适当的积分速率方程拟合到放射性标记底物跨膜平衡的时间进程来计算转运的动力学参数。尿苷和胸苷的转运符合具有方向对称性但负载和空载载体迁移率不同的简单载体模型。从零转运流入和平衡交换通量的比较中可以明显看出，在从不同个体获得的一批红细胞中，负载载体的移动速度比空载载体快3至18倍。不同批次的红细胞最大平衡交换速度也不同。将细胞在4℃下储存4天，或用氧化剂或还原剂处理细胞，或将细胞悬浮在低渗溶液中，对核苷转运体的动力学性质没有影响。当所有测试的天然核糖核苷和脱氧核糖核苷在转运体的反侧以远高于米氏常数的浓度存在时，会加速尿苷的流入和流出，而当它们以这些浓度存在于顺侧时会抑制尿苷的流入，但碱基没有显著影响。
