| To determine if any human proteases act this way , we first studied plasma prekallikrein since it can copurify with IGFBP 3 , and found : 1 ) [ 125 ] IGFBP 3 binds to prekallikrein immobilized either on nitrocellulose or on immunocapture plates ; 2 ) the IGFBP 3 heparin binding domain participates in forming the IGFBP 3 / prekallikrein complex ; 3 ) the binary IGFBP 3 / prekallikrein complex can bind IGF 1 to form a ternary complex ; and 4 ) activation of prekallikrein to alpha kallikrein by Factor XIIa resulted in proteolysis of bound IGFBP 3 . 0.77014918^^^ |