The sodium-stimulated adenosine-triphosphatase activity and other properties of cerebral microsomal fractions and subfractions

1.The rat conjugates thyroxine chiefly with glucuronic acid and to a very small extent also with sulphuric acid and with an unidentified substance.2. After the administration of radioactive thyroxine the rat excretes larger amounts of thyroxine glucuronide and smaller amounts of 3,3',5'-triiodothyronine glucuronide in the bile than the dog does.3. Previous studies showing that deiodination of thyroxine from the 3'-or 5'-position is decreased in rats after receiving thiouracil have been confirmed.4. Deiodination from the 3-or 5-position of thyroxine is increased in rats given a diet contain- ing 0-1 % of thiouracil for 28 days or longer.This may account in part for the marked reduction in calorigenic activity of thyroxine administered to thiouracil-treated rats.The L-thyroxine, L-tri-iodothyronine and tetraiodo- thyroacetic acid used as markers on the chromatograms were gifts from Dr A. E. Heming of Smith, Kline and French Laboratories, Philadelphia; the 3,3',5'-tri-iodo-DL-thyronine and 3,3'-di-iodo-DL-thyronine were gifts from Dr R. L.