Woodruff N R, Neet K E
Biochemistry. 1986 Dec 2;25(24):7967-74. doi: 10.1021/bi00372a027.
Pheochromocytoma (PC12) cells have been found to differ from dorsal root ganglionic cells with respect to the modulation of the beta nerve growth factor (beta NGF) binding properties elicited by alpha NGF and gamma NGF. In contrast to our previous results with intact dorsal root ganglionic cells in which only high-affinity binding was blocked, alpha NGF and gamma NGF were found to block competitively all steady-state binding of iodinated beta NGF to PC12 cells at both 37 and 0.5 degrees C. The EC50 that was found for the alpha NGF displacement was 9-10 microM, and the gamma NGF effect had an EC50 of 200 nM, in the predicted range based upon the apparent Kd for dissociation of the alpha beta or the beta gamma complex in solution. The concurrence of the binding EC50 and the Kd for each complex indicates that the formation of alpha beta or beta gamma complexes in solution competes with the process of PC12 receptor binding with 125I-beta NGF. Experiments were carried out examining the dissociation kinetics following the addition of excess unlabeled beta NGF or alpha NGF at both 37 and 0.5 degrees C. Three dissociation components were observed with alpha NGF, in contrast to the two normally found with beta NGF. Lowering the chase temperature to 0.5 degrees C changed the relative contributions made by each component without dramatically changing any of the rate constants. The "slow" receptor was further examined by the dependence on 125I-beta NGF concentration of the slowest component with a chase of either excess alpha NGF or excess gamma NGF at 0.5 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
已发现嗜铬细胞瘤（PC12）细胞在α神经生长因子（αNGF）和γ神经生长因子引发的β神经生长因子（βNGF）结合特性调节方面与背根神经节细胞不同。与我们之前对完整背根神经节细胞的研究结果相反（在完整背根神经节细胞中只有高亲和力结合被阻断），发现在37℃和0.5℃时，αNGF和γNGF均可竞争性地阻断碘化βNGF与PC12细胞的所有稳态结合。αNGF置换的半数有效浓度（EC50）为9 - 10μM，γNGF的效应半数有效浓度为200 nM，这在基于溶液中αβ或βγ复合物解离的表观解离常数（Kd）预测范围内。每种复合物的结合EC50和Kd的一致性表明溶液中αβ或βγ复合物的形成与PC12受体与125I-βNGF的结合过程相互竞争。在37℃和0.5℃下添加过量未标记的βNGF或αNGF后，进行了解离动力学实验。与通常在βNGF中发现的两个解离成分不同，在αNGF中观察到三个解离成分。将追踪温度降至0.5℃改变了每个成分的相对贡献，但没有显著改变任何速率常数。通过在0.5℃下用过量αNGF或过量γNGF追踪时最慢成分对125I-βNGF浓度的依赖性，进一步研究了“慢”受体。
