p018

Thyroxine-binding Globulin of Odd Toed Hoofed Mammals: Characterization of Binding Properties and Heat Stability

Skubella N, Boesser J, 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 and a member of the superfamily of serine proteinase inhibitors (serpins). To characterize its properties in odd toed mammals (order perissodactyla) we examined TBG from different species of the three families equidae: horse (equus caballus), african wild donkey (equus africanus somalienis) and zebra (equus grevyi), tapiridae: tapir (tapirus terrestris) and rhinocerotidae: southern white rhinocerus (ceratothenium simum simum) by Catchard analysis and heat stability of T4-binding. TBG of all perissodactyla had a binding affinity comparable to human TBG but their serum concentration was reduced to 20 to 30% of the human control. The heat stability of all perissodactyla TBGs was much lower than human TBG. No significant differences of T4–binding, serum concentration or heat stability of TBG within the different perissodactyla species was found. These results indicate a very high conservation of this protein in the order perissodactyla.

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