IGF-1 LR3

An 83-amino-acid synthetic analog of insulin-like growth factor-1 (CAS 946870-92-4) combining an Arg3->Glu substitution with a 13-residue N-terminal extension (MFPAMPLLSLFVN) added to native IGF-1's 70-residue sequence. Binds the IGF-1 receptor with full agonist activity but has drastically reduced affinity for IGFBP-3, raising the free-active fraction ~3x and extending circulating half-life to 20-30 hours vs. ~12-15 hours for native IGF-1. Widely used in cell culture as a serum-free supplement to drive proliferation; not FDA-approved for human therapeutic use (distinct from mecasermin rinfabate / Iplex, which is an IGF-1/IGFBP-3 complex).