Fei Y J, Nara E, Liu J C, Boyd C A, Ganapathy V, Leibach F H
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912-2100, USA.
Biochim Biophys Acta. 1999 May 12;1418(2):344-51. doi: 10.1016/s0005-2736(99)00046-2.
We investigated the interaction of rat PEPT2, a high-affinity peptide transporter, with neutral, anionic, and cationic dipeptides using electrophysiological approaches as well as tracer uptake methods. D-Phe-L-Gln (neutral), D-Phe-L-Glu (anionic), and D-Phe-L-Lys (cationic) were used as representative, non-hydrolyzable, dipeptides. All three dipeptides induced H+-dependent inward currents in Xenopus laevis oocytes heterologously expressing rat PEPT2. The H+:peptide stoichiometry was 1:1 in each case. A simultaneous measurement of radiolabeled dipeptide influx and charge transfer in the same oocyte indicated a transfer of one net positive charge into the oocyte per transfer of one peptide molecule irrespective of the charged nature of the peptide. We conclude that the zwitterionic peptides are preferentially recognized by PEPT2 as transportable substrates and that the proton/peptide stoichiometry is 1 for the transport process.
我们采用电生理方法以及示踪摄取法，研究了大鼠高亲和力肽转运体PEPT2与中性、阴离子和阳离子二肽之间的相互作用。以D-苯丙氨酸-L-谷氨酰胺（中性）、D-苯丙氨酸-L-谷氨酸（阴离子）和D-苯丙氨酸-L-赖氨酸（阳离子）作为代表性的、不可水解的二肽。所有这三种二肽在异源表达大鼠PEPT2的非洲爪蟾卵母细胞中均诱导出H⁺依赖性内向电流。每种情况下H⁺与肽的化学计量比均为1:1。在同一个卵母细胞中同时测量放射性标记二肽的流入和电荷转移表明，无论肽的带电性质如何，每转移一个肽分子就有一个净正电荷转移到卵母细胞中。我们得出结论，两性离子肽作为可转运底物被PEPT2优先识别，并且在转运过程中质子/肽的化学计量比为1。
