title: Differential sensitivity of brain iodothyronine 5'-deiodinases to sulfhydryl-blocking reagents.
abstract: Propylthiouracil (PTU) and iodoacetate (IAc) partially inhibit the 5'-deiodination of 3,3',5'-triiodothyronine (rT3) in cerebral cortex, but PTU has no effect on the 5'-deiodination of thyroxine (T4). We now report that pretreatment of cerebral cortex microsomes with increasing concentrations of IAc or iodoacetamide inhibits the PTU-sensitive 5'-deiodination of rT3 with half-maximal inhibition at less than 1 microM IAc. PTU-insensitive 5'-deiodination of rT3 and T4 requires 100-1000-fold higher concentrations of IAc to achieve similar inhibition. Trypsinization decreases both 5'-deiodinating activities by greater than 90%. These data suggest that enzyme SH groups do not participate in the 5'-deiodination of T4 or rT3 by the PTU-insensitive pathway.
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology*; D007453:Iodide Peroxidase / Q000378:metabolism*; D007460:Iodoacetamide / Q000494:pharmacology*; D007461:Iodoacetates / Q000494:pharmacology*; D019807:Iodoacetic Acid; D008297:Male; D010544:Peroxidases / Q000378:metabolism*; D011441:Propylthiouracil / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013965:Thyroidectomy; D014285:Triiodothyronine, Reverse / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D007461:Iodoacetates; D014285:Triiodothyronine, Reverse; D011441:Propylthiouracil; D010544:Peroxidases; D007453:Iodide Peroxidase; D014357:Trypsin; D019807:Iodoacetic Acid; D007460:Iodoacetamide