Properties of the Specific Binding of 125I-Nerve Growth Factor to Responsive Peripheral Neurons

Abstract

The interaction of nerve growth factor (NGF) with its receptor(s) on the surface membranes of responsive chick embryo sympathetic and sensory neurons has been examined using 1251-NGF prepared by a solid phase iodination technique.The specific binding of lz51-NGF to both types of neurons is a complex process.It is nonsaturable at concentrations of i*51-NGF as high as lo-* M and displays apparent multiple affinities (KA Z lOlo to lo6 liters per mole).The specific binding is rapid (kl = 7.5 X 106 M-' s-l at 24') and reversible (kel = 3.8 x lo-' s-l at 24").Native NGF at a concentration of 2 x 10m7 M accelerates the dissociation of bound lz51-NGF 30.fold at 24" (native NGF k-* = 1.2 x 10F2 s-i), suggesting that the apparent multiple affinities for the binding of 1251-NGF are due to a negatively cooperative interaction of NGF receptors.Insulin, at a concentration of 2 x 10m7 M, inhibits the specific binding of 1251-NGF 15 to 20%.Lower or higher concentrations of insulin were not as effective.The material specifically binding '251-NGF comigrates with the surface membrane label iz51-cu-bungarotoxin in two subcellular fractionation procedures.The total amount of specific binding material and the binding per microgram of tissue protein vary during embryonic development in a manner reflecting the temporal pattern of biological responsiveness of sympathetic and dorsal root ganglia.