Figure 2.

Different ligands that activate EGFr via either direct binding or transactivation elicit differing patterns of tyrosine residue phosphorylation in the cytoplasmic tail of the receptor. EGF and TGF-α both induce phosphorylation of six specific residues, albeit to different extents (as indicated by size of the circled letter P). Carbachol activates both the release of TGF-α as well as tyrosine phosphatases such as protein tyrosine phosphatase 1B (PTP1B) that serve to dephosphorylate specific residues.