Molecular Nutrition Unit, Technical University of Munich, Am Forum 5, 85350 Freising-Weihenstephan, Germany.
Amino Acids. 2010 Mar;38(3):753-61. doi: 10.1007/s00726-009-0280-5. Epub 2009 Mar 31.
Influx of [(3)H]-L-proline into renal OK cells revealed that basal transport was mediated by the transporter SIT1. When cells were submitted for 8 h to amino acid deprivation, uptake of L-proline was now dominated by a low-affinity system with an apparent K (m) of 4.4 +/- 0.6 mM and a V (max) of 10.2 +/- 0.6 nmol/mg of protein/min operating in addition to the high-affinity SIT1 system with a K (m) of 0.12 +/- 0.01 mM and a V (max) of 0.28 +/- 0.04 nmol/mg of protein/min. The low- and high-affinity proline transporting systems were sensitive to inhibitors of JNK and PI-3 kinases, whereas a GSK-3 inhibitor affected only the upregulated transport system. Ion-replacement studies and experiments assessing substrate specificities for both systems provided strong evidence that SNAT2, that showed two- to threefold increased mRNA levels, is the responsible transporter mediating the increased proline influx under conditions of amino acid deprivation.
用 [(3)H]-L-脯氨酸 influx 法检测到 OK 细胞中的基础转运是由 SIT1 转运体介导的。当细胞被氨基酸剥夺处理 8 小时后，L-脯氨酸的摄取现在主要由低亲和力系统主导，其表观 Km 为 4.4 +/- 0.6 mM，Vmax 为 10.2 +/- 0.6 nmol/mg of protein/min，此外还有高亲和力 SIT1 系统，Km 为 0.12 +/- 0.01 mM，Vmax 为 0.28 +/- 0.04 nmol/mg of protein/min。低亲和力和高亲和力脯氨酸转运系统对 JNK 和 PI-3 激酶抑制剂敏感，而 GSK-3 抑制剂仅影响上调的转运系统。离子替代研究和评估两种系统底物特异性的实验为 SNAT2 提供了有力证据，SNAT2 的 mRNA 水平增加了两到三倍，是在氨基酸剥夺条件下增加脯氨酸内流的负责转运体。
