Glossary
IGF-1
IGF-1 is a 70-residue peptide, made mostly in the liver, that carries growth hormone signalling. Its receptor, its binding proteins and why LR3 and DES exist.
IGF-1 — insulin-like growth factor 1, once called somatomedin C — is a single-chain polypeptide of 70 amino acids containing three disulfide bridges and resembling proinsulin in structure. The liver produces most of it under the influence of growth hormone, with additional local production in muscle, bone and other tissues, and it relays the bulk of growth hormone’s downstream anabolic signalling.
Receptor and control of availability
IGF-1 acts on the IGF-1 receptor, a tyrosine kinase related in structure to the insulin receptor, which switches on PI3K/Akt and MAPK pathways. In contrast to most peptide hormones, nearly all of it circulates in bound form — more than 95% is held by IGF binding proteins, chiefly IGFBP-3 together with the acid-labile subunit — which lengthens its half-life in circulation from minutes to hours and regulates how much reaches tissues.
The logic of IGF-1 analogs
Research analogs are designed to interfere with precisely this binding. IGF-1 LR3 carries an extra 13 residues at the N-terminus plus an Arg3 substitution, cutting IGFBP affinity dramatically; IGF-1 DES(1-3) deletes the first three residues to reach the same goal by another path.
Related terms
growth hormone secretagogue · somatostatin. Browse IGF and muscle peptides or compare in IGF-1 LR3 vs IGF-1 DES.