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Calcium-Binding Protein Protocols Calcium-Binding Protein Protocols

Calcium-Binding Protein Protocols Calcium-Binding Protein Protocols

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Deconvolution of <strong>Calcium</strong>-<strong>Binding</strong> Curves 31<br />

Fig. 2. Graphical representation of Eqs. 12–14 with k 1 = k 2 = c = 1 (A) and k 1 = 1,<br />

k 2 = 0,001, and c = 250 (B). X-axis represents the normalized concentration of the<br />

ligand and y-axis, the normalized amplitude of the signal (s 1 ■, v ◆, and s 2 ▲).<br />

of a protein with a high-affinity and a low-affinity site with strong positive<br />

coupling between the two (see Fig. 2B).<br />

In the first case, all three curves are identical. In the second case, the Ca 2+ -<br />

binding curve is akin to the previous one, but the curves associated with the<br />

occupancy of site 1 and site 2 are, respectively, left-shifted and right-shifted. In<br />

this latter model, upon ligand titration, the first site is occupied before the second<br />

site. However, the mean number of bound ligand is the same as for a pro-

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