The iron-binding site of transferrin in Figure 17-7 can accommodate certain other metal ions besides Fe₃₊ and certain other anions besides CO₃^2-. Data are given in the table for the titration of transferrin (3.57 mg in 2.00 mL) with 6.64 mM Ga³⁺ solution in the presence of the anion oxalate, C₂O₄^2-, and in the absence of a suitable anion. Prepare a graph similar to Figure 17-10, showing both sets of data. Indicate the theoretical equivalence point for the binding of one and two Ga³⁺ ions per molecule of protein and the observed end point. How many Ga³⁺ ions are bound to transferrin in the presence and in the absence of oxalate?

Figure 17-7

Figure 17-10

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Titration in presence of C,03- Titration in absence of anion Total pL Ga+ added 241 nm Total µL Ga+ added 241 nm Absorbance at Absorbance at 0.0 0.044 0.0 0.000 2.0 0.143 2.0 0.007 4.0 0.222 6.0 0.012 6.0 0.306 10.0 0.019 8.0 0.381 14.0 0.024 10.0 0.452 18.0 0.030 12.0 0.508 22.0 0.035 14.0 0.541 26.0 0.037 16.0 0.558 18.0 0.562 21.0 0.569 24.0 0.576