Plasminogen (Plg) can be converted into active plasmin by tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), kallikrein, and factor XII (Hageman factor). Plasmin can dissolve fibrin blood clots, act on many other processes such as embryonic development, tissue remodeling, inflammation and tumor invasion. Plasmint also can activates collagenases, weakens the walls of the Graafian follicle, cleaves fibrin, fibronectin, thrombospondin, laminin, and von Willebrand factor. Besides, Actin Beta (ACTb) has been identified as an interactor of Plg, thus a binding ELISA assay was conducted to detect the interaction of recombinant rat Plg and recombinant rat ACTb. Briefly, Plg were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to ACTb-coated microtiter wells and incubated for 2h at 37ºC. Wells were washed with PBST and incubated for 1h with anti-Plg 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 37ºC. Finally, add 50 μl stop solution to the wells and read at 450nm immediately. The binding activity of of Plg and ACTb was in a dose dependent manner.