In vitro Conversion of Thyroxin to Triiodothyronine by Kidney Slices.

Chromatographically pure I131 labelled 1-thyroxin was added to surviving kidney slices which were incubated in a modified Krebs-Ringer phosphate solution. 2. Following incubation, the slices were homogenized, extracted with butanol and the thyroxin and triiodothyronine separated and identified by paper chromatography. 3. The triiodothyronine was found to be radioactive. This was taken as evidence of deiodination of thyroxin to triiodothyronine. 4. Conversion of thyroxin to triiodothyronine was reduced by excess iodide and abolished by boiling the tissue or by the addition of potassium cyanide to the media.