Characteristics of Partially Purified Nerve Growth Factor Receptor

Abstract: Receptors for the nerve growth factor protein (NGF) have been isolated from three cell types [embryonic chicken sensory neurons (dorsal root sensory ganglia; DRG), rat pheochromocytoma (PC 12) and human neuroblastoma (LAN‐1) cells] and have been shown to be similar with respect to equilibrium dissociation constants. The present results demonstrate that there are multiple molecular weight species for NGF receptors from DRG neurons and PC 12 cells. NGF receptors can be isolated from DRG as four different molecular species of 228, 187, 125, and 112 kilodaltons, and PC 12 cells as three molecular species of 203, 118, and 107 kilodaltons. The NGF receptors isolated from DRG show different pH‐binding profiles for high‐and low‐affinity binding. High‐affinity binding displays a bell‐shaped pH profile with maximum binding between pH 7.0 and 7.9, whereas low‐affinity binding is constant between pH 5.0 and 9.1, with a twofold greater binding at pH 3.6. At 22°C, the association rate constant was found to be 9.5 ± 1.0 ± 10⁶M^‐1 S^‐1. Two dissociation rate constants were observed. The fast dissociating receptor has a dissociation rate constant of 3.0 ± 1.5 ± 10^‐2 S^‐1, whereas the slow dissociating receptor constant was 2.4 ± 1.0 ± 10^‐4S^‐1. The equilibrium dissociation constants calculated from the ratio of dissociation to association rate constants are 2.5 ± 10^‐11M for the high‐affinity receptor (type I) and 3.2 ± 10^‐9M for the low‐affinity receptor (type II). These values are the same as those determined by equilibrium experiments on the isolated receptors. The data are consistent with the hypothesis that there are at least two different receptors for NGF.