Procollagen I N-Terminal Propeptide is specific for cartilaginous tissues. It is essential for the normal embryonic development of the skeleton, for linear growth and for the ability of cartilage to resist compressive forces, which was are associated with achondrogenesis, chondrodysplasia, early onset familial osteoarthritis, Langer-Saldino achondrogenesis, SED congenita, Kniest dysplasia, Stickler syndrome type I, and spondyloepimetaphyseal dysplasia Strudwick type. A functional binding ELISA assay was conducted to detect the interaction of recombinant rat PINP with recombinant human COL5a2. Briefly, biotin-linked PINP were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to COL5a2-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30 min, 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 rat PINP with recombinant human COL5a2 was shown in Figure 1, the EC50 for this effect is 9.18 ug/mL.