Abstract
Sex steroid binding proteins were identified in hatchling female and male Chelonia mydas by dialysis and steady-state gel electrophoresis when examined at 4°C. A testosterone binding protein with high binding affinity (K a = 0.98 ± 0.5 × 108 M−1) and low to moderate binding capacity (B max = 7.58 ± 4.2 × 10−5 M) was observed in male hatchlings. An oestradiol binding protein with high affinity (K a = 0.35 ± 1.8 × 108 M−1) and low to moderate binding capacity (B max = 0.16 ± 0.5 × 10−4 M) was identified in female hatchlings. This study confirmed that sex steroid binding proteins (SSBPs) become inactivate in both sexes at 36°C, the maximum body temperature of sea turtle hatchlings at emergence. The inactivation of SSBPs at this temperature indicates that sex steroid hormones circulate freely in the body of the green turtles and are biologically available in the blood plasma. This observation is consistent with female and male hatchling C. mydas having different physiological (hormonal) and developmental requirements around the time of emergence. Moreover, concurrently conducted competition studies showed that sex steroids including testosterone and oestradiol do compete for binding sites in both male and female C. mydas hatchling plasma. Competition also occurred between testosterone and dihydrotestosterone for binding sites in the male C. mydas plasma. However, competition studies in the plasma of female hatchling C. mydas demonstrate that oestrone does not compete with oestradiol for binding sites.
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Abbreviations
- SSPAGE:
-
Steady-state polyacrylamide gel electrophoresis
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Acknowledgments
We are grateful to Dr. J. Whittier for her constructive comments about this paper. The Animal Ethics Committee of the University of Queensland, acting in accordance with the Australian Code of Practice approved all experiments (Number ANTA/220/05/UQ-ARC/Earthwatch/URG), and the CITES numbers (Number 46805) acquired from the Malaysian Fisheries Department.
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Communicated by I.D. Hume.
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Ikonomopoulou, M.P., Ibrahim, K. & Bradley, A.J. Sex steroid binding proteins in the plasma of hatchling Chelonia mydas . J Comp Physiol B 178, 837–843 (2008). https://doi.org/10.1007/s00360-008-0271-y
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DOI: https://doi.org/10.1007/s00360-008-0271-y