IGF-1 LR3

IGF-1 LR3 is an 83-residue recombinant analog of insulin-like growth factor I (CAS 143045-27-6, molecular weight about 9,118 g/mol). It combines two modifications: a 13-residue N-terminal extension, derived from the first amino acids of methionyl porcine growth hormone followed by a Val-Asn dipeptide, and substitution of arginine for the glutamate normally at position 3. Both changes reduce association with the IGF-binding proteins, the six-member family that in circulation regulates how much free growth factor is available to reach type 1 IGF receptors.

IGF-1 LR3 in the research literature

Comparative work on the recombinant fusion analogs established the mechanism behind the potency difference. In rat L6 myoblasts, [Arg3]-IGF-I and the long forms were more potent than authentic IGF-I at stimulating protein and DNA synthesis and inhibiting protein breakdown, yet bound bovine IGF-binding protein-2 very poorly and the type 1 receptor slightly less well than IGF-I; the authors concluded that reduced binding-protein association, not increased receptor affinity, explains the difference. Potency ranking in cell lines that secrete binding proteins followed the same logic.

In avian satellite cells and embryonic myoblasts, by contrast, the LR3 analog was less active than native IGF-I and competed less well for receptor binding.