igf-1 lr3 igf-1 lr3 long arginine 3-igf-1, abbreviated as igf-1 lr3 or lr3-igf-1, is a synthetic protein and lengthened analogue of human insulin-like growth factor 1 (igf-1). it differs from native igf-1 in that it possesses an arginine instead of a glutamic acid at the third position in its amino acid sequence ("arginine 3"), and also has an additional 13 amino acids at its n-terminus (mfpampllslfvn) ("long"), for a total of 83 amino acids (relative to the 70 of igf-1). the consequences of these modifications are that igf-1 lr3 retains the pharmacological activity of igf-1 as an agonist of the igf-1 receptor, has very low affinity for the insulin-like growth factor-binding proteins (igfbps), and has improved metabolic stability. as a result, it is approximately three times more potent than igf-1, and possesses a significantly longer half-life of about 20–30 hours (relative to igf-1's half-life of about 12–15 hours). igf-1 lr3clinical dataother nameslong r3-igf-1;igf-1 long r3routes ofadministrationinjectionatc codenonepharmacokinetic dataelimination half-life56-72 hoursidentifierscas number143045-27-6 ychemspidernoneuniim9l22y19h9chemical and physical dataformulac400h625n111o115s9molar mass9117.60 g·mol−1 the amino acid sequence of igf-1 lr3 is mfpamplssl fvngprtlcg aelvdalqfv cgdrgfyfnk ptgygsssrr apqtgivdec cfrscdlrrl emycaplkpa ksa.