A closer look at the signaling complexes. A, VEGF and PlGF binding results in the activation of both receptor monomers. Each receptor monomer is the substrate for the kinase domain of the other. Changing kinase-substrate pairs can result in distinct signaling. B–J, Phosphorylation of VEGFR1 and VEGFR2 by VEGF, VEGF and PlGF in equal quantities (+) and VEGF with PlGF in 10-fold excess (++). R1*1V, VEGFR1 activated by VEGF-VEGFR1; R1*1P, VEGFR1 activated by PlGF-VEGFR1; R1*2, VEGFR1 activated by VEGF-VEGFR2; R2*2, VEGFR2 activated by VEGF-VEGFR2; R2*1, VEGFR2 activated by VEGF-VEGFR1.