A preprohormone is the precursor protein to one or more prohormones, which are in turn precursors to peptide hormones. It contains a signal peptide, the hormone(s) itself (themselves), and intervening amino acids. Before the hormone is released from the cell, the signal peptide and other amino acids are removed.

All peptide hormones are initially synthesized as longer precursors, or preprohormones, on ribosomes attached to the cytosolic surface of the endoplasmic reticulum (ER).

Peptide hormones are synthesized in endoplasmic reticulum, transferred to the Golgi and packaged into secretory vesicles for export. They can be secreted by one of two pathways: Regulated secretion: The cell stores hormone in secretory granules and releases them in “bursts” when stimulated.

ADH is a nonapeptide derived from the preprohormone called prepropressophysin, which contains a signal peptide, neurophysin II, and a glycoprotein. In the Golgi apparatus, the signal peptide portion is cleaved from prepropressophysin to produce a prohormone stored in secretory vesicles.

Signal recognition particle (SRP) binds to the signal peptide as it emerges from the ribosome. SRP brings the ribosome to the ER by binding to a receptor on the ER surface. The receptor is associated with other proteins that make a pore. Translation continues, and the growing amino acid chain slides into the ER lumen.

A sequence of amino acid residues bound at the amino terminus of a nascent protein during protein translation, which when recognized by the signal recognition particle results in the transport of the nascent protein to the organelle of destination.

Peptide hormones are synthesized as precursors and posttranslational modifications such as proteolytic processing, tyrosine sulfation, proline hydroxylation, and hydroxyproline arabinosylation are generally required for their functional mature forms, in particular for the small signaling peptides.