Localization and enzyme activity of iodotyrosine dehalogenase 1 during metamorphosis of frog Microhyla ornata.

The distribution and activity of iodotyrosine dehalogenase 1 (DEHAL1) enzyme was determined during metamorphosis of the frog Microhyla ornata. Immunohistochemical and enzymatic studies in the thyroid, olfactory system, brain, skin, and tail of frog were performed. DEHAL1-positive cells were seen in the olfactory epithelium, the nucleus infundibularis ventralis, the ventricular lining, cerebellum in the brain, in the pituitary gland, in the mucus glands of skin, and in epithelial cells of tadpole tail fin. During metamorphosis, DEHAL1 enzyme activity was also detected in the above-mentioned frog tissues with the enzyme exhibiting higher activity on diiodotyrosine (DIT) as compared to monoiodotyrosine (MIT). Using DIT as a substrate, maximal activity was detected at stage 44 in the brain (157.7 U/mg protein), while it was higher at stage 42 in the tail (138.5 U/mg protein). With MIT as a substrate, highest activity was detected in the brain at stage 42 (65.8 U/mg protein). Thus, the localization, relative levels, and specificity of DEHAL1 suggest that it might be involved in tissue-specific deiodination of MIT and DIT, thus making free iodine available, and therefore plays an essential role during metamorphosis in M. ornata.