Peptide hormone

Peptide hormones are

nuclear) to act within their nuclei

Like all peptides, peptide hormones are synthesized in

vesicles, which can be secreted from the cell by exocytosis in response to specific stimuli (e.g. an increase in Ca²⁺ and cAMP concentration in cytoplasm).^[2]

These prohormones often contain superfluous amino acid residues that were needed to direct folding of the hormone molecule into its active configuration but have no function once the hormone folds. Specific endopeptidases in the cell cleave the prohormone just before it is released into the bloodstream, generating the mature hormone form of the molecule. Mature peptide hormones then travel through the blood to all of the cells of the body, where they interact with specific receptors on the surfaces of their target cells.

Some

neuropeptides" may be used as neurotransmitters in the nervous system

in addition to acting as hormones when released into the blood.

When a peptide hormone binds to a receptor on the surface of the cell, a

second messenger appears in the cytoplasm, which triggers signal transduction leading to the cellular responses.^[3]

Some peptides (angiotensin II, basic fibroblast growth factor-2, parathyroid hormone-related protein) also interact with intracellular receptors located in the cytoplasm or nucleus by an intracrine mechanism.^[4]