Flow-through partial-filling affinity capillary electrophoresis can estimate binding constants of neutral ligands to receptors via a competitive assay technique

This work evaluates the use of a competitive binding assay using flow-through partial-filling affinity capillary electrophoresis (FTPFACE) to estimate binding constants of neutral ligands to a receptor. We demonstrate this technique using, as a model system, carbonic anhydrase B (CAB, EC 4.2.1.1) and arylsulfonamides. In this technique, the capillary is first partially filled with a negatively charged ligand, a sample containing CAB and two noninteracting standards, and a neutral ligand, then electrophoresed. Upon application of a voltage the sample plug migrates into the plug of negatively charged ligand (L(-)) resulting in the formation of a CAB-L(-) complex. Continued electrophoresis results in mixing between the neutral ligand (L(0)) and the CAB-L(-) complex. L(0) successfully competes out L(-) to form the new CAB-L(0) complex. Analysis of the change in the relative migration time ratio (RMTR) of CAB relative to the noninteracting standards, as a function of neutral ligand concentration, yields a value for the binding constant. These values are in agreement with those estimated using other binding and ACE techniques. Data demonstrating the quantitative potential of this method is presented.

Estimation of receptor-ligand interactions by the use of a two-marker system in affinity capillary electrophoresis

The study of receptor-ligand interactions by affinity capillary electrophoresis (ACE) requires an accurate form of analysis. Here, we examine the use of two noninteracting standards (markers) in the analysis of binding constant data in ACE studies. This concept is demonstrated using two model systems: carbonic anhydrase B (CAB, EC 4.2.1.1) and arylsulfonamides, and vancomycin (Van) from Streptomyces orientalis and the dipeptide N-acetyl-d-Ala-d-Ala. In this procedure a plug of receptor and noninteracting standards is injected, and analysis of the change in the relative migration time ratio of the receptor, relative to the noninteracting standards, as a function of the concentration of the ligand yields a value for the binding constant. The findings described here demonstrate that data from ACE studies can best be analyzed using two noninteracting standards, yielding values comparable to those estimated using other binding and ACE techniques.