IGF-BPs control the distribution, function and activity of IGFs in various cell tissues and body fluids. Currently, there are seven named IGF-BPs that form high-affinity complexes with both IGF-I and IGF-II. IGF-BP1 is a 25.4 kDa, cysteine-rich, secreted protein expressed in the liver, deciduas, kidneys, and in amniotic fluid, where it is the most abundant IGF-BP. Levels of IGF-BP1 in serum are lowest after food consumption. IGF-BP1 binds to both IGF-I and IGF-II with equal affinity. Phosphorylated IGF-BP1 hinders IGF actions, whereas nonphosphorylated IGF-BP1 is stimulatory. Recombinant Human IGF-BP1 is a 25.4 kDa protein consisting of 235 amino acid residues (Isoform A).