Hauser M, Donhardt A M, Barnes D, Naider F, Becker J M
Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996-0845, USA.
J Biol Chem. 2000 Feb 4;275(5):3037-41. doi: 10.1074/jbc.275.5.3037.
We have identified an oligopeptide transporter in the yeast Saccharomyces cerevisiae which mediates the uptake of tetra- and pentapeptides, including the endogenous opioids leucine enkephalin (Tyr-Gly-Gly-Phe-Leu) and methionine enkephalin (Tyr-Gly-Gly-Phe-Met). The transporter is encoded by the gene OPT1. Yeast expressing OPT1 can utilize enkephalins to satisfy amino acid auxotrophic requirements for growth. The transport of radiolabeled leucine enkephalin exhibits saturable kinetics, with a K(m) of 310 microM. Transport activity is optimum at acidic pH and sensitive to reagents which uncouple oxidative phosphorylation, suggesting an energy dependence on the proton gradient. Growth, transport, and chromatographic data indicate that leucine enkephalin is not hydrolyzed in the extracellular medium and as such is translocated intact across the cell membrane. The system is specific for tetra- and pentapeptides and can be inhibited by the opioid receptor antagonists naloxone and naltrexone. To date, this is the first example of a eukaryotic transport system which can use enkephalins as a substrate, opening the possibility that a homologue exists in higher eukaryotes.
我们在酿酒酵母中鉴定出一种寡肽转运体，它介导四肽和五肽的摄取，包括内源性阿片样物质亮氨酸脑啡肽（Tyr-Gly-Gly-Phe-Leu）和甲硫氨酸脑啡肽（Tyr-Gly-Gly-Phe-Met）。该转运体由OPT1基因编码。表达OPT1的酵母可以利用脑啡肽来满足生长所需的氨基酸营养缺陷型需求。放射性标记的亮氨酸脑啡肽的转运表现出饱和动力学，K(m)为310微摩尔。转运活性在酸性pH下最佳，并且对解偶联氧化磷酸化的试剂敏感，这表明能量依赖于质子梯度。生长、转运和色谱数据表明，亮氨酸脑啡肽在细胞外培养基中不被水解，因此完整地跨细胞膜转运。该系统对四肽和五肽具有特异性，并且可以被阿片受体拮抗剂纳洛酮和纳曲酮抑制。迄今为止，这是真核生物转运系统中第一个可以将脑啡肽用作底物的例子，这为高等真核生物中存在同源物开辟了可能性。
