3′-Monoidothyronine degradation in rat liver homogenate: Enzyme characteristics and documentation of deiodination by high-pressure liquid chromatography

Robert C. Smallridge, Nancy E. Whorton

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

Characteristics of 3′-monoiodothyronine (3′-T1) degradation were examined in vitro in rat tissue homogenates. In rat liver homogenates, 3′-T1 degradation was optimal at pH 7.4, and was dependent upon time, temperature, and tissue concentration. The Michaeli's constant (Km) = 0.84 μmol/L. 3′-T1 degradation was enhanced by dithiothreitol and inhibited by propylthiouracil, sodium ipodate, ANS, and sodium azide but not by methimazole. Animals that fasted for three days had signficant reductions in both hepatic T4 to T3 conversion (199 ± 12 v 116 ± 12 pg T3 generated/mg protein; P < 0.001) and 3′-T1 degradation (588 ± 31 v 148 ± 53 pg 3′-T1 degraded/mg protein; P < 0.001). To document that 3′-T1 degradation was occurring by deiodination, both liver and kidney homogenates were incubated with 125I-3′-T1 (∼ 3 μCi; 13.1 nmol/L). The reaction products were separated on a reverse-phase high pressure liquid chromatography (HPLC) column. In both tissues an iodide peak was generated, and no other radiolabeled peaks appeared exceptor for 125I-3′-T1. These data suggest that 3′-T1 is metabolized by phenolic-ring monodeiodination and is enzymic in nature.

Original languageEnglish (US)
Pages (from-to)1034-1038
Number of pages5
JournalMetabolism
Volume33
Issue number11
DOIs
StatePublished - Nov 1984

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology

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