Thyroxine 5′-deiodinase activity was studied in male rat Harderian gland homogenates. The reaction rate was proportional to the tissue content in the homogenate and dependent on pH, with an optimum pH of 7.0, and temperature, between 4-37°C. 5′-deiodinase activity was increased by dithiothreitol (DTT) in a dose-dependent manner, and inhibited moderately by propylthiouacil (PTU) and strongly by iopanoic acid (lA). Thyroidectomy enhanced the enzymatic activity (30-fold above the control value) but this increase is totally prevented by the in vivo iopanoic acid treatment. Thyroxine 5′-deiodinase activity was also dependent on T4 concentration (Km = 3.3 nM ; Vmax = 10 fmol 1251-released/mg protein/h) and exhibited a nyctohemeral rhythmicity with a maximal activity at 03.00h (4-fold above basal values) and minimal activity between 12.00-21.00 h.
ASJC Scopus subject areas
- General Biochemistry, Genetics and Molecular Biology
- Pharmacology, Toxicology and Pharmaceutics(all)