Way B A, Furesz T C, Schwarz J K, Moe A J, Smith C H
The Edward Mallinckrodt Department of Pediatrics, St Louis Children's Hospital, Washington University School of Medicine, Missouri 63110, USA.
Placenta. 1998 May;19(4):323-8. doi: 10.1016/s0143-4004(98)90065-0.
Transport of L-lysine by a cultured placental trophoblast cell line was investigated by characterization of L-[3H]lysine uptake. In the mononuclear form of the BeWo clone b30 choriocarcinoma cell, at least two sodium-independent systems are present. Concentration dependence data were fitted by a two system model with Km values (+/- s.e.) of 2 +/- 0.7 and 94 +/- 31 microM and Vmax values (+/- s.e.) of 0.7 +/- 0.3 and 25 +/- 6.0 nM/mg DNA/min. A portion of sodium-independent uptake was inhibited by the sulphydryl modifying reagent N-ethylmaleimide (NEM). Following NEM treatment, the data were fitted by a single system with Km = 10 +/- 2 microM AND Vmax = 5.1 +/- 0.8 nM/mg DNA/min. In the absence of sodium, NEM-resistant uptake was sensitively inhibited by leucine whereas NEM-sensitive uptake was not inhibited by leucine. It is concluded that like placental basal membrane, the mononuclear BeWo cell possesses two sodium-independent L-lysine transport systems. The high-capacity, NEM-sensitive, leucine-insensitive system resembles the widespread system y+. The high-affinity, NEM-resistant, leucine-sensitive system resembles system b(0,+).
通过对L-[3H]赖氨酸摄取的特性研究，探讨了一种培养的胎盘滋养层细胞系对L-赖氨酸的转运。在BeWo克隆b30绒毛膜癌细胞的单核形式中，至少存在两种不依赖钠的系统。浓度依赖性数据通过双系统模型拟合，Km值（±标准误）为2±0.7和94±31微摩尔，Vmax值（±标准误）为0.7±0.3和25±6.0纳摩尔/毫克DNA/分钟。一部分不依赖钠的摄取被巯基修饰试剂N-乙基马来酰亚胺（NEM）抑制。NEM处理后，数据通过单系统拟合，Km = 10±2微摩尔，Vmax = 5.1±0.8纳摩尔/毫克DNA/分钟。在无钠的情况下，NEM抗性摄取被亮氨酸敏感抑制，而NEM敏感摄取不被亮氨酸抑制。结论是，与胎盘基底膜一样，单核BeWo细胞拥有两种不依赖钠的L-赖氨酸转运系统。高容量、NEM敏感、亮氨酸不敏感的系统类似于广泛存在的系统y+。高亲和力、NEM抗性、亮氨酸敏感的系统类似于系统b(0,+)。
