Figure 1.

The homologous bioactive sequences of peptide systems belonging to the cholecystokinin (CCK) family (upper panel). CCK and the antral hormone, gastrin, are the only mammalian members of the family. Caerulein and phyllocaerulein are identified from frogskin extracts. Cionin is a neuropeptide isolated from the central ganglion of the protochord, ciona intestinalis. Note the unique disulfated sequence, which might suggest that cionin may resemble a common ancestor of CCK and gastrin. The core of the bioactive sequences, the common C-terminal tetrapeptide amide, is boxed. The lower panel shows the bioactive sequences of the insect peptides, the sulfakinins, which display some homology with vertebrate and protochordian members of the CCK family (4, 5). Also their C-terminal tetrapeptide amide sequence is boxed.