Cholecystokinin (pancreozymin). 4. Synthesis and properties of a biologically active analogue of the C-terminal heptapeptide with epsilon-hydroxynorleucine sulfate replacing tyrosine sulfate.

The influence of tyrosine O-sulfate, the 27th residue in the sequence of cholecystokinin (pancreozymin) (CCK-PZ), on the contraction of gall bladder of guinea pigs and on the release of amylase in isolated pancreatic cells of the same animal was studied with an analogue of the biologically active C-terminal heptapeptide, CCK-PZ-(27--33). In the new analogue, tyrosine O-sulfate was replaced by epsilon-hydroxynorleucine O-sulfate. The synthetic peptide was found a full agonist in these tests, not quite as potent as the unaltered heptapeptide, but much more active than the previously prepared and studied serine O-sulfate containing analogue. Thus, the distance of the sulfate ester group from the peptide backbone has a major influence on the biological activity of CCK-PZ.