Different binding thermodynamics of Ni²⁺, Cu²⁺, and Zn²⁺ to bacitracin A₁ determined by capillary electrophoresis

Abstract

Thermodynamics of the binding of Ni(2+), Cu(2+) and Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis measuring the peptide effective mobility at different pH in the presence of increasing concentration of the three ligands. The affinity follows the order Ni(2+) > Cu(2+) > Zn(2+), with association constant values of (2.3 +/- 0.1)x10(4), (4.9 +/- 0.2)x10(3), and (1.5 +/- 0.1)x10(3) M(-1), respectively. The only model able to rationalize mobility data implies that metal ion binds to the P(0) peptide form. Moreover, mobility values indicated a change of bacitracin A(1) acidic properties on Ni(2+) and Cu(2+) binding, with a shift of the pK(a) of N-terminal Ile-1 from 7.6 to about 5 and of the pK(a) of the delta-amino group of D-Orn-7 from 9.7 to about 7. Even though on Zn(2+) binding a shift of the N-terminal Ile-1 pK(a) was observed, restrictions in the pH range suitable for investigation, due to precipitation phenomena, did not allow establish if the shift of D-Orn-7 lateral chain pK(a) also occurred. Nonetheless, if present, the shift should be limited to the 7.8-9.7 range. Mobility data indicated that the Stokes radius of the complexes is ca. 3 A lower than that of the free peptide. The present results indicate that metal-ion binding to bacitracin A(1) is more complex than previously assumed.

Capillary electrophoresis of inorganic ions: An update

“…In the same experimental arrangement, CE was used to determine the stability constants and kinetic parameters for the complexes of lanthanide ions with 1,4,7,10-tetraazacyclodecane-N',N'',N'''-tetraacetic acid [267]. Similar CE studies have been reported on complex formation between metal ions and bioligands (such as polypeptides [268][269][270] or metal-containing proteins [271]) and on elucidating the mechanism of perrhenate reduction [272], interaction of lower oxidation states of Re with 1-hydroxyethylidenediphosphonic acid [210], and the redox reaction between Fe(II) and desferrioxamine B [273].…”

Recent Developments in Affinity Capillary Electrophoresis: A Review

“…Castagnola et al studied the binding of metal ions (Ni 2+ , Cu 2+ , and Zn 2+ ) to the dodecapeptide bacitracin by ACE [39,40]. In these studies the peptide effective mobility was measured at varying pH in the presence of increasing concentration of metal ion.…”

Recent trends in CE of inorganic ions: From individual to multiple elemental species analysis

“…Through calculating the binding constants between aromatic phosphonic acids and ammonium and potassium cations, the thermodynamic selectivity of complexation was assessed and compared with the data of molecular mechanics [237]. The association constants for the binding of Ni(II), Cu(II), and Zn(II) toward a polypeptide was studied by measuring its effective mobility at different pH and metal concentrations [238]. Transition metal ions were found to play a negative role on DNA genotyping, causing the CE peaks of DNA samples to be poorly resolved [239].…”