Partial-filling affinity capillary electrophoresis (PFACE) is used to examine the binding interactions between two model biological systems: D-Ala-D-Ala terminus peptides to the glycopeptide antibiotic vancomycin (Van) from Streptomyces orientalis, and arylsulfonamides to carbonic anhydrase B (CAB, EC 4.2.1.1, bovine erythrocytes). Using these two systems, modifications in the PFACE technique are demonstrated including flow-through PFACE (FTPFACE), competitive flow-through PFACE (CFTPFACE), on-column ligand synthesis PFACE (OCLSPFACE), and multiple-step ligand injection PFACE (MSLIPFACE). In PFACE small plugs of sample are injected into the capillary column and an equilibrium is established between receptor and ligand during electrophoresis. Binding constants are then obtained by Scatchard analysis using changes in the migration time of the receptor/ligand on changing the concentration of the ligand/receptor. Data demonstrating the quantitative potential of these methods are presented. This review focuses on the unique capabilities of the different PFACE techniques as applied to two model biological systems.
Binding constants between the glycopeptides teicoplanin (Teic) and ristocetin (Rist) and their derivatives to D-Ala-D-Ala terminus peptides were determined by on-column receptor synthesis coupled to partial-filling affinity capillary electrophoresis (PFACE) or affinity capillary electrophoresis (ACE). In these techniques, the column is first partially filled with increasing concentrations of D-Ala-D-Ala terminus peptides. This is followed by plugs of buffer, antibiotic and two noninteracting standards, and acetic and/or succinic anhydride (and buffer in the case of ACE). The order of the reagent plugs containing the antibiotic and anhydride varies with the charge of the glycopeptide. Upon electrophoresis, the antibiotic reacts with the anhydride yielding a derivative of Teic or Rist. Continued electrophoresis results in the overlap of the derivatized antibiotic and the plug of D-Ala-D-Ala peptide. Analysis of the change in the relative migration time ratio (RMTR) of the new glycopeptide relative to the standards, as a function of the concentration of the D-Ala-D-Ala ligand yields a value for the binding constant K(b). The techniques described here can be used to assess how the derivatization of drugs alters their affinities for target molecules.
SummaryBinding constants belween the antibiotic ristocetin A (Rist A) and D-Ala-D-Ala terminus peptides were determined using affinity capillary electrophoresis (ACE). In these experiments ~o techniques are used to obtain binding constants. In the first, a plug of RistAand non-interacting standards are injected and electrophoresed. Analysis of the change in the relative migration time ratio (RMTR) of Rist, relative to the non-interacting standards, as a function of the concentration of peptide, yields a value for the binding constant (Kb). In the second, samples of peptide and standards are injected and electrophoresed in increasing concentrations of Rist A in the running buffer. Analysis using the RMTRyields a Kb. The findings described here demonstrate the advantage of using ACE for estimating binding parameters be~een antibiotics and ligands.
Afffinity capillary electrophoresis (ACE) is a new analytical technique that has been shown to be an efficient and accurate tool in studying biomolecular noncovalent interactions and determining binding and dissociation constants of formed complexes. ACE uses as its basis the change in migration time of a receptor upon binding to a ligand found in the electrophoresis buffer. Subsequent Scatchard analysis using noninteracting markers realizes a binding constant. Herein, ACE and three modifications in the technique, partial-filling ACE (PFACE), flow through PFACE (FTPFACE), and multiple-step ligand injection ACE (MSLIACE) are used to probe the binding of ristocetin A (Rist A) and vancomycin (Van) from Streptomyces orientalis to D-Ala-D-Ala terminus peptides and carbonic anhydrase B (CAB, E.C.4.2.1.1) to arylsulfonamides.
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