FIGURE 19-10 Biological relationship between three PDGF iso-forms and two PDGF receptors. Arrows show the binding affinities for each dimerized receptor. The amino acid sequence homology (%) between a and /3-PDGF receptors is shown in each domain. Abbreviations: LB, ligand binding; TM, transmembrane; JM, juxta membrane; TK, tyrosine kinase; Ki, kinase insert; C, carboxy terminal. Human chromosomal location is shown in parentheses. Reproduced with permission from Matsui, T. (1994). Platelet derived growth factor system in human oncogenesis and its signaling pathways. In "Growth Factors: Cell Growth, Morphogenesis, and Transformation." (T. Nakamura and K. Matsumoto, eds.), Gann Monograph on Cancer Research pp. 42, 1-12, Japan Scientific Societies Press, Tokyo, CRC Press, Boca Raton/Ann Arbor/London/Tokyo.

NGF binds to two receptor types, one of which is high affinity and the other is low affinity. The latter is found in lymphocytes and macrophages, and both forms may derive from a single gene. The tyrosine kinase receptor, trk, is found in neural tissues

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