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. Author manuscript; available in PMC: 2009 Nov 15.
Published in final edited form as: Biochem J. 2008 Nov 15;416(1):77–84. doi: 10.1042/BJ20081059

Figure 6. Constants for the binding of ferric or calcium ions to phosphorylated CCK8.

Figure 6

Equilibrium constants for the binding of ferric or calcium ions to CCK8PO4 (CCKP) were obtained by fitting the data in Figures 1B and 5A, respectively, to a two-site ordered model with the program BioEqs. Absorbance ratios are given relative to the absorbance of CCK8PO4 at 275 nm in the absence of added metal ions. Values in italics were the best estimates obtained by simulation of the data in Figure 5B for ferric ion binding in the presence of calcium ions as described in Experimental. Binding of a Ca2+ ion to the first site enhances not only the changes in absorption on binding of a ferric ion to the second site by 2.5-fold, but also the affinity of ferric ions for the second site by 500-fold.