Differences in receptor binding and stability to enzymatic digestion between cck-8 and cck-58

Introduction and Aims It has been proposed that distinct tertiary structures of the C-terminus of CCK-8 and CCK-58 result in differences in stimulation of pancreatic amylase secretion. Binding of CCK-8 and CCK-58 to CCK-A and CCK-B receptors and stability to enzymatic digestion were used as independent probes for tertiary structure of the C-terminus. Methodology Canine CCK-58 was purified from intestinal extracts and CCK-8 was purchased. Their amounts were determined by amino acid analysis. The effect of tertiary structure on receptor binding at CCK-A receptors and CCK-B receptors was evaluated using membrane preparations from mouse pancreas and brain. The influence of C-terminal tertiary structure on stability to enzymatic digestion was evaluated by reacting CCK-8 and CCK-58 with endopeptidase 24:11. Results CCK-58 was three times more potent than CCK-8 for binding mouse pancreatic membrane CCK-A receptors and equipotent to CCK-8 for binding mouse brain CCK-B receptors. CCK-8 was readily digested by endopeptidase 24:11, whereas CCK-58 was not. Conclusions The results strongly support the hypothesis that differences in tertiary structure of the carboxyl terminus of CCK-8 and CCK-58 influence receptor binding and stability to enzymatic digestion.