G-protein linked melatonin binding sites in the chicken lung

[125I]Iodomelatonin binding was first demonstrated in the chicken lung membrane preparations. The binding was saturable, reversible, rapid, and of high affinity. The sites of binding distributed widely in different subcellular fractions except the cytosol fraction. Scatchard plots are linear indicating a dissociation constant (Kd) of 8.11 +/- 0.73 pmol/l and a maximum number of binding sites of 1.29 +/- 0.16 fmol/mg protein (n = 9). The Kd estimated from the kinetic study was 11.2 pmol/l. Guanosine 5'-O-(3-thiotriphosphate) significantly increased the Kd values while the density of binding sites was not affected indicating that the binding sites may be linked to a guanine nucleotide binding protein.