3'-Monoiodothyronine Degradation in Rat Liver Homogenate: Enzyme Characteristics and Documentation of Deiodination by High-Pressure Liquid Chromatography

摘要

Characteristics of 3'-monoiodothyronine (3'-T sub 1) degradation were examined in vitro in rat tissue homogenates. In rat liver homogeneates, 3' - T sub 1 degradation was optimal at pH 7.4, and was dependent upon time, temperature, and tissue concentration. The km = 0.84 micrometer. 3'-T sub 1 degradation was enhanced by dithiothreitol and inhibited by propylthiouracil, sodium iopdate, ANS, and sodium azide but not by methimazole. Animals fasted for three days had significant reductions in both hepatic T sub 4 to T sub 3 conversion (199 + or - 12 vs. 116 + or - 12 pg T sub 3 generated/mg protein; p less than 0.001) and 3'T sub 1 degradation (588 + or - 31 vs. 148 + or - 53 3'T sub 1 degraded/mg protein; p less than 0.001). To document that 3' T sub 1 degradation was occurring by deiodination, both liver, and kidney homogenates were incubated with 125I-3' T sub 1 (approx. 3 micro Ci; 13.1 nM). The reaction products were separated on a reverse phase HPLC column. In both tissues an iodide peak was generated, and no other radiolabeled peaks appeared except for 125I-3'T sub 1. These data suggest that 3'T sub 1 is metabolized by phenolic ring monodeiodization, and is enzymic in nature. Originator supplied keywords include: 3'-Monoiodothyronine, Deiodination.