Renin (REN) is an enzyme protein. It is mainly secreted by the juxtaglomerular cells of the kidney. Its main function is to cleave angiotensinogen in the blood to produce angiotensin I, thereby initiating the renin-angiotensin-aldosterone system (RAAS), which plays a crucial role in regulating blood pressure and maintaining fluid and electrolyte balance in the body. Besides,Endothelin 1 (EDN1) has been identified as an interactor of REN, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant pig REN and recombinant rat EDN1.Briefly, biotin-linked REN were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100μl were then transferred to EDN1-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 50µl stop solution to the wells and read at 450nm immediately. The binding activity of REN and EDN1 was shown in Figure 1, the EC50 for this effect is 0.41ug/mL.