Temple C S, Stewart A K, Meredith D, Lister N A, Morgan K M, Collier I D, Vaughan-Jones R D, Boyd C A, Bailey P D, Bronk J R
Department of Human Anatomy, University of Oxford, South Parks Road, Oxford OX1 3QX, United Kingdom.
J Biol Chem. 1998 Jan 2;273(1):20-2. doi: 10.1074/jbc.273.1.20.
4-Aminophenylacetic acid (4-APAA), a peptide mimic lacking a peptide bond, has been shown to interact with a proton-coupled oligopeptide transporter using a number of different experimental approaches. In addition to inhibiting transport of labeled peptides, these studies show that 4-APAA is itself translocated. 4-APAA transport across the rat intact intestine was stimulated 18-fold by luminal acidification (to pH 6.8) as determined by high performance liquid chromatography (HPLC); in enterocytes isolated from mouse small intestine the intracellular pH was reduced on application of 4-APAA, as shown fluorimetrically with the pH indicator carboxy-SNARF; 4-APAA trans-stimulated radiolabeled peptide transport in brush-border membrane vesicles isolated from rat renal cortex; and in Xenopus oocytes expressing PepT1, 4-APAA produced trans-stimulation of radiolabeled peptide efflux, and as determined by HPLC, was a substrate for translocation by this transporter. These results with 4-APAA show for the first time that the presence of a peptide bond is not a requirement for rapid translocation through the proton-linked oligopeptide transporter (PepT1). Further investigation will be needed to determine the minimal structural requirements for a molecule to be a substrate for this transporter.
4-氨基苯乙酸（4-APAA）是一种缺乏肽键的肽模拟物，已通过多种不同的实验方法证明其与质子偶联寡肽转运体相互作用。除了抑制标记肽的转运外，这些研究还表明4-APAA自身也会发生转运。通过高效液相色谱（HPLC）测定，管腔酸化（至pH 6.8）可使4-APAA在大鼠完整肠道中的转运增加18倍；用pH指示剂羧基-SNARF荧光法显示，在从小鼠小肠分离的肠细胞中，加入4-APAA后细胞内pH降低；4-APAA可反刺激从大鼠肾皮质分离的刷状缘膜囊泡中放射性标记肽的转运；在表达PepT1的非洲爪蟾卵母细胞中，4-APAA可反刺激放射性标记肽的流出，并且通过HPLC测定，它是该转运体转运的底物。4-APAA的这些结果首次表明，肽键的存在并非通过质子连接寡肽转运体（PepT1）快速转运的必要条件。需要进一步研究以确定分子成为该转运体底物的最小结构要求。
