Fibroblast Growth Factor 19 (FGF19) is a member of the fibroblast growth factor (FGF) family. FGFs are heparin-binding growth factors with a core 120 amino acid (aa) FGF domain that allows for a common tertiary structure. In general, FGFs are expressed during embryonic development and in restricted adult tissues.Human FGF-19 cDNA predicts a 251 aa precursor protein with a 22 aa signal peptide and a 229 aa secreted mature protein with no potential N-linked glycosylation sites. FGF19-FGFR1 is one of paired transcripts mediating the dialogues between extraembryonic membrane and endometrium. Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human FGF19 and recombinant human FGFR1. Briefly, FGF19 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to FGFR1-coated microtiter wells and incubated for 2h at 37℃. Wells were washed with PBST and incubated for 1h with anti-FGF19 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody, wells were aspirated and washed 3 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 μL stop solution to the wells and read at 450 nm immediately. The binding activity of recombinant human FGF19 and recombinant human FGFR1 was shown in Figure 1, the EC50?for this effect is 3.83 ug/mL.