Sokol P P, Holohan P D, Ross C R
Department of Pharmacology, State University of New York, Syracuse.
J Pharmacol Exp Ther. 1987 Nov;243(2):455-9.
The molecular mechanism of the electroneutral organic cation/H+ antiporter in renal brush border membrane vesicles was studied utilizing the prototypic organic cation N1-methylnicotinamide. The hydrophobic carbodiimide, N,N'-dicyclohexylcarbodiimide (DCCD), inactivated organic cation transport irreversibly with an IC50 of 2.6 microM at pH 7.5 and 40 nM at pH 6.0. On the other hand, the hydrophilic reagents, 1-ethyl-3-[3-(dimethylamino)-propyl]carbodiimide and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline, did not affect organic cation transport. Substrate did not affect the rate of the DCCD inactivation which followed pseudo-first-order-kinetics. A double logarithmic plot of the apparent rate constants vs. the DCCD concentration gave a straight line with a slope of 0.8. The data are consistent with a simple bimolecular reaction mechanism and imply that one molecule of DCCD inactivates one carboxylate group per active transport unit and that the carboxylate group is critical for transport.
利用原型有机阳离子N1-甲基烟酰胺研究了肾刷状缘膜囊泡中电中性有机阳离子/H+反向转运体的分子机制。疏水碳二亚胺N,N'-二环己基碳二亚胺（DCCD）在pH 7.5时以2.6 microM的IC50不可逆地使有机阳离子转运失活，在pH 6.0时为40 nM。另一方面，亲水性试剂1-乙基-3-[3-(二甲氨基)丙基]碳二亚胺和N-乙氧基羰基-2-乙氧基-1,2-二氢喹啉不影响有机阳离子转运。底物不影响遵循假一级动力学的DCCD失活速率。表观速率常数与DCCD浓度的双对数图给出一条斜率为0.8的直线。这些数据与简单的双分子反应机制一致，表明每一个活性转运单元中一个DCCD分子使一个羧基失活，并且该羧基对转运至关重要。
