Fig. 7.

Characterization of secretin receptor binding in COS-1 cell membranes. Shown are curves for secretin competition for binding of [¹²⁵I-Tyr¹⁰]secretin to membranes from COS-1 cells expressing the wild-type (WT) and alanine- or cysteine-replacement mutants in the absence and presence of cuprous phenanthroline. Values represent percentages of maximal saturable binding that were observed in the absence of secretin. They are expressed as means ± S.E.M. of duplicate data from three independent experiments.