A building block outside the twenty the body normally uses, introduced deliberately to resist breakdown. It also gives a molecule a distinctive analytical signature.

A peptide three amino acids long. KPV is one.

A peptide four amino acids long.

A peptide five amino acids long.

A peptide seven amino acids long.

A peptide nine amino acids long.

One end of a peptide chain, conventionally written first. Modifications at this end are common and produce a different molecule.

The other end of the chain, conventionally written last.

A longer molecule the body processes into the final active one. Material labeled by precursor number may not correspond to the processed form actually being described.

The portion removed from a precursor during processing. Not the active molecule.