IGF-1 LR3: Insulin-like growth factor long arginine 3 (IGF-1 LR3) is a modified version of insulin-like growth factor-1 (IGF-1). It contains the complete human IGF-I protein sequence with a substitution of arginine for glutamic acid at the third position and has additional 13 amino acids at its N-terminus making it a total of 83 amino acids compared to the 70 of IGF-1. Insulin-like growth factor-1 (IGF-1) is the principal mediator of growth hormone (GH), plays a crucial role in promoting cell growth and differentiation in childhood and continues to have an anabolic effect in adults.
IGF-1 is part of a wide network of growth factors, receptors and binding proteins involved in mediating cellular proliferation, differentiation, and apoptosis. Bioavailability of IGF-1 is affected by insulin-like growth factor binding proteins (IGFBPs) which bind IGF-1 in circulation with an affinity equal to or greater than that of the IGF-1 receptor (IGF-1R). The six IGFBPs serve as carrier proteins and bind approximately 98% of all circulating IGF-1. Other proteins known to bind IGF-1 include ten IGFBP-related proteins (IGFBP-rPs), albeit with lower affinities than the IGFBPs. IGF-1 expression levels vary in a number of clinical conditions suggesting it has the potential to provide crucial information as to the state of an individual’s health.