Figure 6.
Apparent Kd values as a function of pH. pH-dependent Kd values were measured by fluorescence polarization (FP) using N-terminal FITC-fluorophore labeled (A) XRCC1pSpT-18, (B) XRCC1pSpT-24 or (C) XRCC1EpT-18 (pH 7.4: •, ─; pH 7.0: □, ···; pH 6.5: *, —; pH 6.0: △, -·-, pH 5.5: ж, -··-). (D) The titration curves of the three phosphopeptides obtained at pH 7.4 are compared. The FP values were normalized to 1.0 to facilitate comparison of the results. Data were fit to a single-site binding equation as described in Materials and Methods. Studies were performed in 25 mM HEPES, 25 mM MES, 150 mM NaCl, 1 mM EDTA, 2 mM DTT, and 0.05% Tween 20.