Study on Dissociated States of Monocarboxylic Acids and Their Interactions With MCT1 by Capillary Electrophoresis...

High-performance capillary electrophoresis (CE) has been widely applied in the analysis of organic acids, especially monocarboxylic acids (MAs), but no studies on the CE analysis of dissociated states of MAs have been reported. Here, 15 MAs were analyzed by the newly developed universal interface-induced current detector (IICRD). Two current signal peaks were observed in current electrophoretograms (CR-EGs), whereas only one peak with low sensitivity can be obtained by diode array detector (DAD). The current signal peaks of MAs were accurately identified by adding a charge-neutral marker and calculating by pK_a. The qualitative analysis indicated that the two current signal peaks of MAs were charge-neutral forms [MA^±] and monovalent anions [MA^-] in order. Quantitative analysis showed that CE-IICRD can enhance the sensitivity of MA analytes to 40 µM in limit of detection (LOD), with a linear range from 10^-6 to 10^-2 M. Furthermore, interactions between different dissociated states of MAs and monocarboxylate transporter 1 (MCT1) were studied by combined application of nonimmobilized cell CE (NICCE) method for the first time. The binding kinetic parameters and mole number of MCT1 on cell membranes can also be obtained. Besides, competitive binding experiments proved that BAY-8002 (MCT1-specific inhibitor) and lactic acid shared the same binding site. CE-IICRD provides a new method to reveal the interaction between different dissociated forms of MAs or other biomolecules and essential receptors.