Fig. 1
From: Tyrosine modification increases the affinity of gastrin for ferric ions
Tyrosine sulphation of gastrin enhances ferric ion binding. As reported previously, addition of aliquots of ferric chloride to 10 µM gastrin17 (a, down triangle) in 10 mM sodium acetate, 100 mM NaCl, 0.005 % Tween 20, pH 4.0 at 298 K resulted in an increase in the absorption at 280 nm up to a molar ratio of 2. Addition of aliquots of FeCl3 to 10 µM gastrin17SO4 (b, diamond), or gastrin17PO4 (c, up triangle) caused a more gradual change in absorption. Data are expressed as a percentage of the absorbance of that peptide without ferric ions. Points are means of at least three separate experiments; bars represent the SEM. Lines represent the best fit to a two site model with the program BioEqs; the appropriate Kd values are given in Table 1