Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) is one of nine mammalian serine proteases.It is secreted mostly by hepatocytes and to a lesser extent by the intestine, pancreas, kidney, adipose tissue, and vascular cells.PCSK9 can promote the degradation of LDL receptors in the liver, which in turn reduces the liver's ability to clear LDL-C from the bloodstream.Besides,Epidermal Growth Factor (EGF) has been identified as an interactor of PCSK9, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant mouse PCSK9 and recombinant human EGF. Briefly, PCSK9 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to EGF-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-PCSK9 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, 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 450/630nm immediately. The binding activity of recombinant mouse PCSK9 and recombinant human EGF was shown in Figure 1, the EC50 for this effect is 0.111ug/mL.