W. Green
Aug 1, 1968
Citations
2
Influential Citations
30
Citations
Quality indicators
Journal
Endocrinology
Abstract
The effect of several tyrosine derivatives on deiodination of 3,5-diiodo-L-tyrosine (DIT) has been examined in vitro and in vivo. In TPNH-supplemented sheep thyroid homogenates, the most effective inhibitors of deiodination, in order of increasing potency, were 3,5-dibromo-L-tyrosine (DBT), 3,5-dinitro- L-tyrosine (DNT) and 3-nitro-L-tyrosine (MNT); kinetic studies suggested purely competitive inhibition. Compounds with weak or no inhibitory activity included tyrosine itself, its 3-methyl-, 3-isopropyl-, 3-ra-propyl-, and 3- amino- derivatives, and 3,4-dihydroxy-L-phenylalanine. DBT, DNT and MNT also inhibited deiodination of DIT by sheep thyroid slices. In rats, administration of DBT, DNT, or MNT with 131I-DIT inhibited deiodination, and led to the appearance of an unknown DIT metabolite in blood and urine. Administration of the most potent in. vitro inhibitor, MNT, to rats prelabeled with radioiodine was followed by the urinary excretion of large amounts of a similar unknown organic iodine compound, tog...