Differences in receptor binding and stability to enzymatic digestion between CCK-8 and CCK-58.
OBJECTIVE
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.


METHODS
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.
Reeve
Joseph R
JR
CURE Digestive Diseases Research Center, VAGLAHS, Los Angeles, CA 90073, USA. jreeve@ucla.edu
McVey
Douglas C
DC
Bunnett
Nigel W
NW
Solomon
Travis E
TE
Keire
David A
DA
Ho
F J
FJ
Davis
Michael T
MT
Lee
Terry D
TD
Shively
John E
JE
Vigna
Steven R
SR
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002766:Cholecystokinin / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D004285:Dogs; D013058:Mass Spectrometry; D051379:Mice; D008969:Molecular Sequence Data; D015260:Neprilysin / Q000378:metabolism; D017434:Protein Structure, Tertiary; D043886:Receptor, Cholecystokinin A; D043887:Receptor, Cholecystokinin B; D011949:Receptors, Cholecystokinin / Q000378:metabolism*; D012844:Sincalide / Q000737:chemistry* / Q000378:metabolism*
D000596:Amino Acids; D043886:Receptor, Cholecystokinin A; D043887:Receptor, Cholecystokinin B; D011949:Receptors, Cholecystokinin; C038823:cholecystokinin 58; D002766:Cholecystokinin; D015260:Neprilysin; D012844:Sincalide