Figure 4.

Comparison of IGF-IR Activation by IGF-I Forms. A, KIRA assay IGF-IR phosphorylation levels by IGF-I in enriched media quantified by immunoblotting. Results are compared with mature IGF-I activation within each KIRA experiment, where each sample was measured in triplicate. Data shown are mean ± SEM for four experiments. B, Calculated contribution of mature IGF-I, pro-IGF-I, and gly-pro-IGF-I to IGF-IR activation. Pro-IGF-I displays equivalent activation of the receptor compared with mature IGF-I, whereas gly-pro-IGF-I has a significantly reduced ability to activate the IGF-IR. *P < .05 for comparisons between conditions.