Surface plasmon resonance analysis of receptor complex formation between Flt-1 and PTK7. (A) A total of 0.5 or 1.0 μg of each purified protein was resolved in 3%-12% Tris-Bis Native Gel, and stained with Coomassie Blue R250 and then destained (R1, Flt-1, R2, Flk-1/KDR). (B) Purified full-length PTK7 (2μM or 4μM) or fragmented PTK7^15-59 (2.3μM or 10μM) was allowed to flow over chips bearing immobilized Flt-1 (B) or KDR (C) at concentrations of 500nM. All sensorgrams were corrected for unbound-chip background. (D) Purified Flt-1 was immobilized at a concentration of 500nM. Full-length PTK7 at different concentrations (0.2, 2 or 4μM) was allowed to flow over the chip surface in the presence or absence of 20 ng/mL VEGF-A. (E) Sensorgram was run with or without PlGF (50 ng/mL) in the same immobilized and analyte conditions described for panel D. All sensorgrams were corrected for unbound-chip background.