Bone Morphogenetic Protein Receptor 2 (BMPR2) is a member of the bone morphogenetic protein (BMP) receptor family of transmembrane serine/threonine kinases. BMPR2 is a TGFβ type II receptor expressed on cumulus cells. Growth Differentiation Factor 9 (GDF9) can bind to BMPR2 through different type I receptors, thereby regulating downstream metabolic reactions. Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human BMPR2 and recombinant human GDF9. Briefly, biotin-linked BMPR2 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to GDF9-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 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 BMPR2 and recombinant human GDF9 was shown in Figure 1, the EC50?for this effect is 42.87 ng/mL.