IGF-1

IGF-1 is insulin-like growth factor 1, a 70-amino-acid single-chain polypeptide with three intramolecular disulfide bonds. It is structurally related to insulin and proinsulin, and its mature form is produced primarily in the liver in response to growth hormone stimulation, although many peripheral tissues also produce IGF-1 locally. IGF-1 is the principal mediator of the anabolic and mitogenic effects that were historically attributed directly to growth hormone, forming the endocrine arm of what is usually called the GH-IGF-1 axis. The foundational discovery of the somatomedin hypothesis and the later renaming of those factors is reviewed in Daughaday & Rotwein, Endocr. Rev. 1989 (NLM 2666112).

Receptor biology

IGF-1 signals principally through the IGF-1 receptor (IGF1R), a receptor tyrosine kinase that is structurally homologous to the insulin receptor and that signals through the insulin receptor substrate (IRS) family, PI3K-AKT, and MAPK pathways. IGF-1 also binds the insulin receptor and hybrid IGF1R-IR receptors with lower affinity, and its bioavailability in circulation is heavily regulated by a family of six high-affinity IGF-binding proteins (IGFBP-1 through IGFBP-6). The majority of circulating IGF-1 is bound to IGFBP-3 and an acid-labile subunit (ALS) in a ternary complex; the free fraction is small. Receptor and binding-protein biology is reviewed in LeRoith et al., Endocr. Rev. 1995 (NLM 7540527).

Why IGF-1 chemistry is tricky

The three disulfide bonds in IGF-1 mean that reduced, scrambled, and oxidized forms with the same amino-acid sequence can have very different folded structures and very different receptor activities. Analytical characterization of IGF-1 research material therefore requires more than intact mass and HPLC purity: it should include evidence that the disulfide pattern is native (typically by peptide mapping after proteolytic digestion under non-reducing conditions, or by ion-mobility MS) and that aggregation is controlled (size-exclusion chromatography). Analog variants such as IGF-1 LR3 (Long R3 IGF-1) add an N-terminal extension and a single substitution that reduces binding to IGFBPs, changing the free-fraction behavior in vitro; these are distinct molecules and should not be cross-identified with native IGF-1.

How Open Assay indexes IGF-1 material

Open Assay indexes IGF-1 and its commonly studied analogs as separate entries, and the characterization fields surfaced on each listing include a flag for whether the disulfide pattern has been confirmed and whether aggregation by SEC is disclosed. These are not routine fields on every COA, and their absence is reported rather than assumed.