FUNCTIONS OF THE HEPATIC GAMMA-GLUTAMYL CYCLE

肝脏γ-谷氨酰循环的功能

• 批准号: 6524023
• 负责人: NAZZARENO BALLATORI
• 金额: $ 23.77万
• 依托单位: UNIVERSITY OF ROCHESTER
• 依托单位国家: 美国
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-09-01 至 2003-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6524023
• 关键词: Xenopus oocyte; biological transport; chemical conjugate; detoxification; digoxin; glutamyltransferase; glutathione; liver function; liver metabolism; membrane transport proteins; molecular cloning; protein structure function; sulfur aminoacid; yeasts

DESCRIPTION: (Adapted from investigator's abstract) Reduced glutathione (GSH) plays a critical role in a multitude of biochemical processes, and disturbances in its homeostasis are implicated in the etiology and progression of a number of diseases. The initial step in the turnover of this tri-peptide in all mammalian cells is its transport into the extracellular space; however, the transport systems that mediate GSH efflux remain poorly defined. In the liver, a major site of GSH synthesis, GSH is released at high rates into both blood plasma and bile. GSH transport into bile functions as a driving force for bile secretion and plays an important role in hepatic detoxification of drugs, metals, and other reactive compounds of both endogenous and exogenous origin. GSH is also released across the sinusoidal membrane into blood plasma for delivery to other tissues. Our recent studies provide important insight into molecular mechanisms of GSH transport. In particular, we demonstrated that oatp1, the sinusoidal organic solute transporter, functions as a GSH/organic solute exchanger. This finding not only identifies the energy coupling mechanism for oatp1, but also elucidates a pathway for GSH release into blood plasma, as well as a novel function for GSH. Moreover, we demonstrated that Ycf1p, the yeast orthologue of mammalian mrp proteins, mediates ATP-dependent, low-affinity GSH transport, indicating that mrp may mediate GSH efflux in mammalian cells. The overall goals of the proposed studies are to identify and characterize GSH and glutathione S-conjugate transport mechanisms, and in particular to test the hypothesis that the oatp- and mrp-family of transporters mediate cellular GSH release. Our specific aims are: (1) Test whether oatp2, a recently cloned transporter that is homologous to oatp1, also mediates GSH/organic solute exchange. (2) Establish the kinetics and specificity of GSH transport on oatp1, and on oatp2 if this transporter is also found to function as a GSH exchanger. (3) Test whether GSH is a substrate or a co-substrate for mrp2, and if so; a) define the energetics of transport on this canalicular membrane protein, b) compare these parameters with those for GSH transport on yeast Ycf1p, and c) examine whether GSH is also a substrate for mrp3 and mrp6, putative hepatocellular lateral membrane proteins; and (4) Continue to define the role of the intrahepatic -glutamyl cycle in the disposition of glutathione S-conjugates and their conversion to the corresponding mercapturic acids by examining mechanisms of mercapturic acid transport.

性状：（改编自研究者摘要）还原型谷胱甘肽（GSH） 在许多生物化学过程中起着关键作用， 在体内平衡中的作用与许多 疾病。在所有的三肽中， 哺乳动物细胞是它的运输到细胞外空间;然而， 介导GSH外排的转运系统仍不清楚。在肝脏中， 作为GSH合成的主要场所，GSH以高速率释放到血液和血液中， 血浆和胆汁。GSH转运到胆汁中作为胆汁的驱动力， 分泌并在药物的肝脏解毒中起重要作用， 金属以及其他内源性和外源性反应化合物。 GSH也通过窦膜释放到血浆中， 输送到其他组织。我们最近的研究提供了重要的见解， GSH转运的分子机制。特别是，我们证明， oatp 1，正弦有机溶质转运蛋白，作为GSH/有机 溶质交换器这一发现不仅确定了能量耦合 oatp 1的机制，但也阐明了GSH释放到血液中的途径 血浆，以及一个新的功能GSH。此外，我们证明， Ycf 1 p是哺乳动物mrp蛋白的酵母直向同源物，介导ATP依赖性， 低亲和力GSH转运，表明mrp可能介导GSH流出， 哺乳动物细胞 拟议研究的总体目标是识别和表征GSH 和谷胱甘肽S-缀合物转运机制，并且特别是测试 oatp和mrp转运蛋白家族介导细胞GSH的假说 release.我们的具体目标是：（1）检测最近克隆的oatp 2是否 与oatp 1同源的转运蛋白，也介导GSH/有机溶质 交易所(2)建立oatp 1上GSH转运的动力学和特异性， 如果发现oatp 2转运蛋白也起GSH交换剂的作用，则在oatp 2上也是如此。 (3)测试GSH是否是mrp 2的底物或共底物，如果是，a） 定义在该小管膜蛋白上的转运的能量学，B） 将这些参数与酵母Ycf 1 p上GSH转运的参数进行比较，以及c） 检查GSH是否也是推定的mrp 3和mrp 6的底物 肝细胞侧膜蛋白;（4）继续确定作用 肝内谷氨酰循环在谷胱甘肽处置中的作用 S-共轭物和它们通过 检查巯基尿酸转运的机制。