IGF-1 LR3

IGF-1 LR3 — short for Long R3 insulin-like growth factor 1 — is a recombinant analogue of human IGF-1 with 83 amino acids, defined by two engineered changes: position 3 carries arginine where the natural protein has glutamate, and an extra stretch of 13 residues is added to the N-terminus. Together these raise the molecular weight to about 9118 g/mol and, more importantly, greatly weaken binding to the IGF binding proteins, which in the blood normally hold on to more than 95% of IGF-1.

Vials contain 0.1 mg or 1 mg — small by our standards, because cell culture uses it at nanomolar levels and one milligram covers an enormous number of plates. With a molecular weight of 9117.60 g/mol, 1 mg equals about 110 nanomoles; dissolved in 1 mL that makes a stock of around 110 micromolar, which is then diluted several thousand times. At these working levels, noticeable amounts stick to plastic tubes and pipette tips, so dilute stocks are usually made up with a carrier protein — commonly 0.1% bovine serum albumin. Published use is mainly in culture with little or no serum, in proliferation assays with myoblasts and other cells, and in studies of IGF-1 receptor signalling where binding proteins from serum would otherwise distort the results.