期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1973
卷号：70
期号：12
页码：3884-3888
DOI：10.1073/pnas.70.12.3884
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Iodination of the {beta} nerve growth factor protein up to 4.1 iodines per mole of nerve growth factor was achieved with no loss of biological activity. At this level of incorporation no native or monoiodo nerve growth factor remained, the major species being the tri- and tetraiodo derivatives. An 125I-labeled {beta} nerve growth factor of high specific activity containing 0.5 iodine per mole of {beta} nerve growth factor was used to determine the specific binding of nerve growth factor to dorsal root ganglion cells of 8-day-old embryonic chicks. The specific binding of 125I-labeled nerve growth factor reached saturation at 30-50 ng/ml and half-saturation at 7-8 ng/ml (0.26 nM). The number of receptors per responsive medio-dorsal cell was calculated to be about 2 x 104. The pattern of displacement of bound 125I-labeled {beta} nerve growth factor by native {beta} nerve growth factor showed that the two proteins had identical affinities for the receptor. The specificity of the binding for {beta} nerve growth factor was demonstrated by the fact that only native {beta} nerve growth factor displaced the bound 125I-labeled form. Partially inactivated derivatives of {beta} nerve growth factor retained the same fraction of their specific-binding capacity as of their biological activity. The specificity of the binding for cell type was shown by the lack of any specific component of 125I-labeled {beta} nerve growth factor binding to liver or brain cells. The rate constant for association of {beta} nerve growth factor with its receptor, k1, was 1.0 x 107 mol-1 sec-1 and the rate constant for dissociation, k-1, 1.2 x 10-8 sec-1.
