Table 1

Ferric binding protein characterization for different exogenous anions: Fe3+nFbpX

Fe3+nFbpX, Xn− =[Xn−]50/M*Relative affinityλmax/nm, ɛ/M−1⋅cm−1Keff/M−1§E1/2/mV
Phosphate1.0  × 10−61.0481 (2,430)4.2  × 1018−300
Arsenate7.9  × 10−60.15476 (2,280)1.3  × 1018−251
Pyrophosphate9.5  × 10−60.13472 (2,770)1.9  × 1017−212
NTA2.3  × 10−40.0052468 (3,460)2.2  × 1017−184
Citrate3.5  × 10−40.0034474 (1,770)1.4  × 1017−191
Oxalate4.2  × 10−40.0029475 (3,570)3.7  × 1017−186
Carbonate2.4  × 10−20.000050
  • * Concentration of competing anion Xn− required to displace 50% of bound POEmbedded Image from Fe3+nFbpPO4 at the following conditions: [POEmbedded Image] = 1 μM, [NaCl] = 200 mM, pH = 6.5, 0.05 M Mes, T = 25°C. See equilibrium reaction 4

  • Binding affinity of various Xn− for Fe3+nFbp to form Fe3+nFbpX relative to Xn− = POEmbedded Image

  • Absorption maximum and molar absorptivity for Fe3+nFbpX in the visible region at pH 6.5, 0.2 M KCl, and 0.05 M Mes. 

  • § Effective stability constants corresponding to reaction 5 at pH 6.5, 0.05 M Mes, 0.2 M KCl, and 20°C. Results obtained from equilibrium competition experiments (Eqs. 2 and 3) are an average of two to four independent determinations at 10:1 to 0.5:1 EDTA:Fe3+nFbpX ratios. 

  • Uncorrected Fe3+/2+ half potentials (E1/2) for Fe3+nFbpX at pH 6.5, 0.05 M Mes, 0.2 M KCl, and 20°C. 

  • No carbonate binding was observed at pH 6.5 at 10 mM [COEmbedded Image]; reported values for binding affinity were obtained at pH 8.