Fig. 2
From: Tyrosine modification increases the affinity of gastrin for ferric ions
Tyrosine sulphation of gastrin enhances CCK2 receptor binding. The ability of gastrin17 (down triangle), gastrin17SO4 (diamond), or gastrin17PO4 (up triangle), to compete with [125I]-Bolton and Hunter labelled-CCK8SO4 (150 pM, 100,000 cpm) for binding to the human CCK1 (a) or CCK2 (b) receptor on transiently transfected COS-7 cells was measured as described in “Methods”. Points represent the mean data from at least three experiments, each in triplicate, and lines represent the best fit to a one site model. None of the three peptides competed with [125I]-CCK8SO4 for binding to the CCK1 receptor. The IC50 values for the binding of gastrin17, gastrin17SO4 and gastrin17PO4 to the CCK2 receptor were 61 ± 32, 1.2 ± 0.4 and 58 ± 20 nM, respectively. In contrast to the previously reported enhancement of binding to both receptors on sulphation of CCK8, phosphorylation had no effect on the peptide’s affinity for the CCK2 receptor