Partial Purification of Rat Serum Thyroxine-Binding Globulin

Abstract

Rats have been frequently used experimentally in various aspects of thyroid research, but their serum-binding proteins for thyroid hormones (TH) remain unclear compared with those of human beings. Previous studies showed that in rats the major serum TH-binding protein was electrophoretically slow migrating prealbumin (R-TBPA) (1). Davis et al. (2) reported the presence of rat serum thyroxine-binding globulin (R-TBG) using polyacrylamide gel slab electrophoresis, but other studies showed little or no R-TBG (3,4). In special conditions such as on feeding rats a low protein, high carbohydrate diet (4) or on fasting (5), the rats were reported to gain clear R-TBG band. Thus, R-TBG has not yet been purified, and its binding characteristics have not been determined. We report that R-TBG was partially purified using Sephadex G-200 gel filtration from hypothyroid rat serum and its binding characteristics determined by charcoal-binding method.