Modulation of the neuronal binding of the β subunit of nerve growth factor (NGF) by the α-NGF subunit

✍ Scribed by Nathaniel R. Woodruff; Kenneth E. Neet

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 474 KB
• Volume: 19
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.240190304

✦ Synopsis

Abstract

The effect of the α subunit of the 7S‐NGF on the binding of β‐NGF to its two classes of sites on target cells has been studied. The presence of μM concentrations of α‐NGF causes the displacement of ^125^I‐β‐NGF from one class of sites on dissociated dorsal root ganglia neurons from stage E9 chicken embryos. At O.1 nM ^125^I‐β‐NGF, increasing α‐NGF concentrations produce a monotonic displacement curve with half‐maximal displacement occurring at 10 μM α‐NGF. The affinity and number of sites of the ^125^I‐β‐NGF displaced by α‐NGF are similar to those of β‐NGF that binds to the higher affinity (site I) receptors. The binding to the lower affinity class of sites (site II) is not affected‐by concentrations of α‐NGF up to 30 μM. This modulation of ^125^I‐β‐NGF binding does not occur with equivalent concentrations of serum albumin. No detectable neuronal binding of ^125^I‐β‐NGF was found, suggesting that the mechanism does not involve direct competition for receptor sites. The dissociation constant for the α‐β complex is in the μM range, and formation of this complex in solution can thus compete with the process of ^125^I‐β‐NGF binding to neurons. A model accounting for these observations includes binding of the α‐β complex to the lower affinity but not to the higher affinity sites. We conclude that there are differences in the specificity of the two classes of receptors.