• A Assessment of proteolytic activity present in culture media of human embryonic kidney 293T cells transfected with cDNA encoding PAPP-A2, PAPP-A2(D643fs) (family 1), or PAPP-A2(A1033V) (family 2). Radiolabeled substrates tested include IGFBP-3, IGFBP-4, and IGFBP-5. Cleavage was visualized by autoradiography following SDS-PAGE. Positions of intact IGFBPs (i) and cleavage products (c) are indicated. 