Cholecystokinin (CCK) is widely distributed in the central nervous system and the gastrointestinal tract. The 33-amino acid peptide contains a carboxyl terminal octapeptide sequence Asp-Tyr-Met-Gly-Trp-Met-Asp-Phe-NH2 which confers the biological activity of CCK, and where the tyrosine residue occurs in sulfated form. This octapeptide, CCK8(SO3), has high affinity for the two structurally-defined CCK receptors types, CCK1 and CCK2.
CCK-SAP is a chemical conjugate of sulfonated CCK and the ribosome-inactivating protein, saporin. It specifically eliminates cells that express CCK Receptor.