Pan Y, Wong E A, Bloomquist J R, Webb K E
Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
J Nutr. 2001 Apr;131(4):1264-70. doi: 10.1093/jn/131.4.1264.
We determined the primary structure, tissue distribution and in vitro functional characterization of a peptide transporter, oPepT1, from ovine intestine. Ovine PepT1 (oPepT1) cDNA was 2829-bp long, encoding a protein of 707 amino acid residues with an estimated molecular size of 78 kDa and an isoelectric point (pI) of 6.57. Transport function of oPepT1 was assessed by expressing oPepT1 in Xenopus oocytes using a two-electrode voltage-clamp technique. The transport process was electrogenic and pH dependent, but independent of Na+, Cl- and Ca2+. The oPepT1 displayed a broad substrate specificity for transport of neutral and charged dipeptides and tripeptides. All dipeptides and tripeptides examined evoked inward currents in a saturable manner, with an affinity constant (Kt) ranging from 27 micromol/L to 3.0 mmol/L. No responses were detected from tetrapeptides or free amino acids. Northern blot analysis demonstrated that oPepT1 was expressed in the small intestine, omasum and rumen, but was not expressed in liver and kidney. The presence of the peptide transporter in the forestomach at such levels could provide nutritionally important amino acid nitrogen to ruminants.
我们确定了来自绵羊肠道的一种肽转运体oPepT1的一级结构、组织分布及体外功能特性。绵羊PepT1（oPepT1）cDNA长2829 bp，编码一个由707个氨基酸残基组成的蛋白质，估计分子大小为78 kDa，等电点（pI）为6.57。采用双电极电压钳技术在非洲爪蟾卵母细胞中表达oPepT1，以此评估其转运功能。转运过程是生电的且依赖于pH，但不依赖于Na⁺、Cl⁻和Ca²⁺。oPepT1对中性和带电荷的二肽及三肽的转运具有广泛的底物特异性。所有检测的二肽和三肽均以饱和方式诱发内向电流，亲和常数（Kt）范围为27 μmol/L至3.0 mmol/L。未检测到四肽或游离氨基酸的反应。Northern印迹分析表明，oPepT1在小肠、瓣胃和瘤胃中表达，但在肝脏和肾脏中不表达。前胃中存在这种肽转运体，可为反刍动物提供营养上重要的氨基酸氮。
