STUDIES FOR THE MECHANISM OF MULTIPLICITY IN SUBSTRATE SPECIFICITY OF TRANSPORTERS.

药代动力学特征对于充分的药物治疗很重要，并且受到许多因素的影响，包括结合蛋白、药物代谢酶和膜转运蛋白。其中，药物转运蛋白对于药物的肠道吸收、组织分布以及肝、肾排泄具有重要作用。因此，重要的是接受哪种药物作为每种转运蛋白的底物。然而，一些药物转运蛋白接受多种化合物作为底物，并且尚未阐明药物转运蛋白的这种多特异性的机制。有机阳离子/肉碱转运蛋白OCTN和有机阴离子转运多肽OATP-C也接受多种生理和药物化合物作为底物。在本研究中，我们通过关注这些转运蛋白的多功能性，研究了这些转运蛋白底物识别的多特异性机制。OCTN 转运肉碱作为生理底物，阳离子化合物作为异生素。当OCTN运输肉碱时，它仅表现出Na+依赖性，而有机阳离子如四乙铵(TEA)的运输则不依赖于Na+。使用OCTN突变蛋白的研究表明，肉毒碱和TEA部分共享OCTN2上的底物识别位点，但它们并不相同。 Na + 很大程度上影响肉碱对OCTN2的亲和力，而TEA没有表现出Na + 对OCTN2的亲和力有任何改变。然而，肉碱和TEA表现出相互抑制作用，但不能用完全竞争性抑制动力学来解释。肉碱和TEA之间的转运机制的差异可以通过肉碱特异性的羧基部分的存在来解释，并且Na 2 影响肉碱的羧基部分和OCTN2蛋白之间的相互作用。这些观察结果表明，OCTN 的多特异性是由于 OCTN 通过改变取决于底物的传输机制（关于驱动力 Na^）而实现的多功能性。因此，阐明每种基质的转运蛋白的驱动力对于阐明转运蛋白的多特异性机制很重要。就OATP而言，目前尚未明确证明驱动力，而OATP接受各种化合物作为底物。为了阐明 OATP 多特异性的机制，未来有必要确定每种底物的驱动力 Less

Pharmacokinetic characteristics are important for the adequate drug therapy and they are affected by many factors, including binding proteins, drug metabolizing enzymes and membrane transporters. Among them, drug transporter are important for the intestinal absorption, tissue distribution, and hepatic and renal excretion of drugs. Accordingly, it will be important what kinds of drugs are accepted as substrates for each transporter. However, some drug transporters accept various compounds as substrates and it has not been clarified the mechanism for such multispecificity of drug transporterOrganic cation/carnitine transporter OCTN and organic anion transporting polypeptide OATP-C also accept various physiological and drug compounds as substrates. In the present study, we studied the mechanism for the multispecificity in the substrate recognition of those transporters by focusing on the multifunctionality of themOCTN transports carnitine as physiological substrates and cationic compounds … More as xenobiotics. When OCTN transports carnitine, it exclusively shows Na^+-dependence, while the transport of organic cation such as tetraethylammonium (TEA) is Na^+-independent. The study using mutant protein of OCTN exhibited that carnitne and TEA partially shares the substrate recognition sites on OCTN2, while they are not identical. Na^+ largely affect the affinity of carnitine to OCTN2, while TEA did not show any change in the affinity to OCTN2 by Na^+. However, carnitine and TEA exhibited mutual inhibitory effect, while they are not explained by complete competitive inhibition kinetics. The difference in the transporting mechanism between carnitine and TEA could be explained by the presence of the carboxylmoiety that is specific for carnitine and the Na^+ affect the interaction between carboxylmoiety of carnitine and OCTN2 protein. These observations suggested that multispecificity of OCTN is due to the multifunctionality of OCTN by changing the transport mechanisms depending on the substrates, regarding the driving force, Na^+. Accordingly, clarification of the driving force of the transporter for each substrate is important to clarify the mechanism of multispecificity of transporters. In the case of OATP, at present no driving force has been clearly demonstrated, while OATP accept various compounds as substrates. To clarify the mechanism for the multispecificity of OATP, it will be essential to identify the driving force for each substrate in future Less