Figure 1.

Schematic representation of human endogenous opioid families and their main functional peptides after precursor processing. For each family of peptides, the following information is reported: (i) the names of the genes (PENK, PDYN, POMC, and PNOC); (ii) the amino acid sequence of the preforms (NCBI Reference Sequence is reported in brackets next to the proform names); (iii) on the right, the names of the main functional peptides highlighted with a corresponding colour in the preform peptide sequence and in the isolated peptide sequence when it is required.