p017

Thyroxine-binding Globulin of Marine Mammals (Order Cetacea)

Boesser J, Skubella N, Fingerhut A, Janssen OE

Dept. of Endocrinology, Center of Internal Medicine, University of Essen, Essen, Germany

Thyroxine-binding globulin (TBG) is the main transport protein for thyroid hormones in mammals. To characterize its properties in cetacea, we examined serum from Tursiops truncatus (bottlenose dolphin), Cephalorhynchus commersonii (commerson's dolphin), Inia geoffrensis (pink river dolphin), Phocoena phocoena (harbor porpoise) and Delphinapterus leucas (beluga) by Scatchard analysis and heat stability of T4-binding. Compared to human serum, TBG of the different cetacea species had a slightly reduced binding affinity and greatly reduced heat stability. Sequencing of the TBG-gene from bottlenose dolphin and beluga revealed homology of 82% compared to the human TBG-gene. Phylogenetic analysis of the two cetacean TBG-genes and the known sequences from man, cow, pig, sheep, horse and rat reveal a close relationship of the cetacea with the order artiodactyla (cow, pig, sheep). Our findings support the hypothesis that the aquatic order cetacea is the sister group of the terrestrial order artiodactyla.

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