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  • Title: [125I]iodomelatonin-binding sites in the bursa of Fabricius of birds: binding characteristics, subcellular distribution, diurnal variations and age studies.
    Author: Liu ZM, Pang SF.
    Journal: J Endocrinol; 1993 Jul; 138(1):51-7. PubMed ID: 7852892.
    Abstract:
    The melatonin-binding sites in membrane preparations of the bursa of Fabricius of birds were studied using [125I]iodomelatonin as a radioligand. The binding sites were stable, saturable, reversible and of high affinity. Scatchard analysis of specific binding revealed equilibrium binding constants (Kd) of (means +/- S.E.M.) 43.1 +/- 5.9, 73.3 +/- 7.6 and 35.3 +/- 4.8 pmol/l respectively at the mid-point of the light period (mid-light) in chickens, pigeons and quail, with a total number of binding sites (Bmax) of 1.23 +/- 0.15, 1.33 +/- 0.18 and 0.94 +/- 0.07 fmol/mg protein. The diurnal variation in [125I]iodomelatonin binding showed that the Bmax was 45, 115 and 70% higher at mid-light than at mid-dark in the bursae of chickens, pigeons and quail respectively. The Kd value determined from kinetic analysis was 49.0 +/- 6.4 pmol/l at mid-light in the chicken bursa. The [125I]iodomelatonin-binding sites of chicken bursal membranes had the following order of pharmacological affinities: 2-iodomelatonin > melatonin > 6-chloromelatonin > 6-hydroxymelatonin > N-acetyl-serotonin > 5-hydroxytryptamine, tryptamine, 5-methoxytryptophol, 1-acetylindole-3-carboxaldehyde, 3-acetylindole, L-tryptophan, 5-hydroxyindole-3-acetic acid, 5-hydroxytryptophan suggesting that the [125I]iodomelatonin-binding sites were highly specific for melatonin. The subcellular distribution of binding sites in the chicken bursa was in the following descending order: nuclear > mitochondrial > microsomal > cytosolic fraction. There was an age-related decrease in [125I]iodomelatonin-binding in chicken bursal membranes, with higher densities in the neonate.(ABSTRACT TRUNCATED AT 250 WORDS)
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