Characterization of 2-[125i]iodomelatonin binding sites in the brain of a marsupial, bennett's wallaby (macropus rufogriseus rufogriseus)

Abstract 1. 1. Specific high affinity binding of 2-[ 125 I]iodomelatonin was detected in the brain of the pouch young of a marsupial, Bennett's wallaby. 2. 2. Binding was rapid, stable, saturable and reversible. 3. 3. Scatchard analysis indicated a single class of high affinity binding sites with an equilibrium dissociation constant (Ay of 68 ± 13 pM, a maximal number of binding sites (β max ) of 0.7 ±0.1 fmol/mg protein and a Hill coefficient ( n H ) of 1.12 ± 0.10. 4. 4. Specific binding was inhibited by GTP (1 mM) indicating that the melatonin receptor is coupled to a guanine nucleotide binding protein, and by melatonin and closely related analogues with a potency order identical to that reported previously in the brain of eutherian mammals, birds and a reptile. 5. 5. These studies suggest that the melatonin receptor is well-conserved through evolution.