IGF-1 (insulin-like growth factor 1, formerly somatomedin C) is a 70-amino-acid single-chain polypeptide with three disulfide bridges and structural homology to proinsulin. It is produced mainly in the liver in response to growth hormone, plus locally in muscle, bone and other tissue, and it carries most of growth hormone's downstream anabolic signalling.
Receptor and regulation
IGF-1 binds the IGF-1 receptor, a tyrosine kinase receptor structurally related to the insulin receptor, activating PI3K/Akt and MAPK signalling. Unlike most peptide hormones it circulates almost entirely bound — over 95% is complexed with IGF binding proteins, principally IGFBP-3 with the acid-labile subunit — which extends its circulating half-life from minutes to hours and controls how much is available to tissue.
Why analogs exist
That binding is exactly what research analogs manipulate. IGF-1 LR3 adds a 13-residue N-terminal extension and an Arg3 substitution that sharply reduces IGFBP affinity; IGF-1 DES(1-3) removes the first three residues for the same purpose by a different route.
Related terms
growth hormone secretagogue · somatostatin. Browse IGF and muscle peptides or compare in IGF-1 LR3 vs IGF-1 DES.