Purine and pyrimidine transport and permeation in human erythrocytes.
Purine and pyrimidine transport and permeation in human erythrocytes.
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嘌呤和嘧啶在人红细胞中的转运和渗透。
DOI：
10.1016/0005-2736(87)90004-6
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Wohlhueter,RM
中科院分区：
文献类型：
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作者：
Plagemann,PG;Woffendin,C;Puziss,MB;Wohlhueter,RM
在25或30°C下，通过快速动力学技术在0.02 - 5000 μM底物范围内测定人红细胞悬液中放射性标记次黄嘌呤、腺嘌呤和尿嘧啶摄取的时间进程。在浓度高于25 μM时，次黄嘌呤和腺嘌呤的细胞内磷酸核糖基化速率相对于其进入细胞的速率不显著，并且可以通过积分速率分析测量和分析底物跨膜平衡的时间过程。次黄嘌呤和尿嘧啶通过简单易化载体转运，具有方向对称性，高容量和Michaelis-Menten常数分别约为0.2和5 mM。腺嘌呤可能是由具有类似性质的载体运输，但没有饱和度可检测到高达5 mM的浓度。胞嘧啶进入细胞的速度比其他三个核碱基慢得多，它的进入似乎不是由载体介导的。次黄嘌呤转运蛋白类似于一组哺乳动物细胞系的转运蛋白，其不表现出与核苷转运蛋白的任何重叠，并且对核苷转运抑制剂具有抗性。核碱基对相互干扰和反向转运的影响的研究结果是复杂的，并且不允许关于所涉及的独立载体的数量的明确结论。浓度低于5 μM时，腺嘌呤和次黄嘌呤的放射性标记在细胞内蓄积至高于平衡水平。这种积累的一部分反映了代谢捕获，特别是当培养基中含有50 mM磷酸盐时。但部分是由于游离腺嘌呤和次黄嘌呤在培养基浓度为1 μM和在无磷酸盐培养基中孵育时的明显集中积累高达3倍。这种集中的积累可能是由于额外的高亲和力，低容量，主动运输系统的腺嘌呤和次黄嘌呤的功能，但其他因素可能是负责，如饱和结合细胞内成分。
Time courses of the uptake of radiolabeled hypoxanthine, adenine and uracil were measured by rapid kinetic techniques over substrate ranges from 0.02 to 5000 μM in suspensions of human erythrocytes at 25 or 30°C. At concentrations above 25 μM, the rate of intracellular phosphoribosylation of hypoxanthine and adenine was insignificant relative to their rates of entry into the cell and time courses of transmembrane equilibration of the substrates could be measured and analyzed by integrated rate analysis. Hypoxanthine and uracil are transported by simple facilitated carriers with directional symmetry, high capacity and Michaelis-Menten constants of about 0.2 and 5 mM, respectively. Adenine is probably transported by a carrier with similar properties but no saturability was detectable up to a concentration of 5 mM. Cytosine entered the cells much more slowly than the other three nucleobases, and its entry seems not to be mediated by a carrier. The hypoxanthine transporter resembles that of one group of mammalian cell lines, which does not exhibit any overlap with the nucleoside transporter and is resistant to inhibitors of nucleoside transport. Results from studies on the effects of the nucleobases on the ifnlux and countertransport of each other were complex and did not allow unequivocal conclusions as to the number of independent carriers involved. At concentrations below 5 μM, radiolabel from adenine and hypoxanthine accumulated intracellularly to higher than equilibrium levels. Part of this accumulation reflected metabolic trapping, especially when the medium contained 50 mM phosphate. But part was due to an apparent concentrative accumulation of free adenine and hypoxanthine up to 3-fold at medium concentrations 1 μM and when cells were incubated in phosphate-free medium. This concentrative accumulation could be due to the functioning of additional high-affinity, low-capacity, active transport systems for adenine and hypoxanthine, but other factors could be responsible, such as saturable binding to intracellular components.