[Demonstration of specific binding sites for carp gonadotropin in ovary membrane preparations of Anguilla (Anguilla anguilla L.)].

Membrane preparations from silver eel ovary bind specifically labeled carp gonadotropin (cGTH 125I); similar preparations from kidney, liver, brain, and muscle exhibit either no or negligible specific binding. cGTH and partially purified eel pituitary extract, but neither hCG nor bTSH, inhibit cGTH 125I specific binding in a dose-dependent way. However, a high membrane concentration can bind hCG 125I and this binding is partly inhibited by excess hCG, thus suggesting the existence of a relatively small number of sites able to recognize this hormone. Studies of either cGTH inhibition of cGTH 125I specific binding or cGTH 125I dose-dependent binding have permitted, according to Scatchard, the binding parameters to be determined. Specific binding seems to have two components: one with low affinity and high capacity, and the other with high affinity (Kd = 1.2 10(-10) M) and low capacity (N = 0.2 fmol/mg ovary).