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. Author manuscript; available in PMC: 2010 Jul 13.
Published in final edited form as: J Biol Chem. 2005 Aug 22;280(45):37782–37789. doi: 10.1074/jbc.M505278200

FIGURE 9. Proposed model for mechanism of action of PAPP-A in myogenesis.

FIGURE 9

PAPP-A cleaves IGFBP-2, leading to generation of a C-terminal (CT) IGFBP-2 fragment and an N-terminal (NT) IGFBP-2 fragment loosely bound to IGFs. The affinity of IGFs with the NT IGFBP-2 fragment is much lower than the affinity of IGFs with intact IGFBP-2 or the affinity of IGFs with type I IGF receptors. Thus, IGFs bound to the NT IGFBP-2 fragment readily dissociate to interact with IGF receptors in myoblasts, thereby leading to enhanced myoblast proliferation and differentiation.