Retinal [I]iodomelatonin binding sites in the tree shrew (Tupaiidae)

The characteristics of melatonin-binding sites labelled by ¹²⁵I]iodomelatonin in membrane preparations from the tree shrew retina were determined. Specific binding of ¹²⁵I]iodomelatonin to the membrane preparations of tree shrew retina was rapid, stable, saturable, and reversible. Among the indoles tested only 6-chloromelatonin, melatonin and N-acetylserotonin had significant affinities to the ¹²⁵I]iodomelatonin binding site. Scatchard analysis of the membrane preparations revealed a dissociation constant (K_d) of 51.0 ± 16 pM and total number of binding sites (B_max) of 1.97 ± 0.6 fmol/mg protein.