Fig. 1.

Three distinct biosynthetic pathways of secreted peptide hormones categorized by their structural characteristics. Secreted peptide hormones can be categorized into the following three groups: peptides involving complex post-translational modifications followed by extensive proteolytic processing; peptides involving intramolecular disulfide bond formation followed by proteolytic processing; and peptides involving multiple intramolecular disulfide bonds without proteolytic processing. The first group of peptides are called small post-translationally modified peptides; the latter two groups are defined as cysteine-rich peptides.