Electrophoretic investigation of interactions of sanguinarine and chelerythrine with molecules containing mercapto group

Using mercaptoethanol and (l)-cysteine as representatives of mercapto compounds and capillary zone electrophoresis as experimental technique, it was evidenced that sanguinarine and chelerythrine do not react with the mercapto group of organic compounds at pH 7.4. Their interaction is fast and reversible complexation based on non-bonding intermolecular interaction in which enter uncharged forms of sanguinarine or chelerythrine. A negatively charged group, either bound to the mercapto ligand or supplied from solution, participates in the complexation. Simple 1:1 interaction scheme reported in literature holds therefore only for mercapto compounds bearing anionic group. Stoichiometric binding constants corrected for the abundance of the uncharged alkaloid form at pH 7.4 are of the order of magnitude of 104 l/mol and depend on both cations and anions of the background electrolyte. Interaction of sanguinarine and chelerythrine with human or bovine serum albumins does not qualitatively differ from their interaction with simple mercapto compounds. Stoichiometric binding constants for the binding of sanguinarine with human and bovine serum albumins in sodium phosphate buffer pH 7.4, corrected for the abundance of the interacting uncharged form, are 332 000±38 400 and 141 000±14 400 l/mol, respectively. The former agrees well with the value K=385 000 (or log K=5.59) from static photometric experiments. Constants for the complexation of uncharged chelerythrine with human and bovine serum albumins are 2 970 000±360 000 and 1 380 000±22 600 l/mol, respectively.