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Equilibrium binding of ¹²⁵I‐nerve growth factor (¹²⁵I‐NGF) to cells coexpressing the tyrosine kinase receptor A (TrkA) and common neurotrophin receptor (p75^NTR), cells coexpressing both receptors where p75^NTR is occupied, and cells expressing only p75^NTR, revealed reciprocal modulation of receptor affinity states. Analysis of receptor affinity states in PC12 cells, PC12 cells in the presence of brain‐derived neurotrophic factor (BDNF), and PC12^nnr5 cells suggested that liganded and unliganded p75^NTR induce a higher affinity state within TrkA, while TrkA induces a lower affinity state within p75^NTR. These data are consistent with receptor allosterism, and prompted a search for TrkA/p75^NTR complexes in the absence of NGF. Chemical crosslinking studies revealed high molecular weight receptor complexes that specifically bound ¹²⁵I‐NGF, and were immunoprecipitated by antibodies to both receptors …