Development of a non-radiometric method for estimation of Iodothyronine 5'- deiodinase type ii Activity in rat brain

Abstract

Iodothyronine 5'-deiodinase type II (DII) is an important enzyme catalyzing the conversion of   about 75% of T₄ to T₃ in brain.  Determination of this enzyme activity reported so far, involved use of hazardous radioactive methods. We have ventured to modify the earlier radioactive method by an exclusively non-radiometric procedure. The cerebral cortex of rats were carefully dissected out, homogenized and centrifuged to obtain a post-mitochondrial preparation for assessing DII activity.The preparation was incubated in a suitable non-radioactive assay medium for T₄ to T₃ conversion. The T₃ formed, was detected and estimated by competitive enzyme immunoassay and DII activity was expressed indirectly in terms of fmoles T₃ formed/min/mg protein. The validity of this method has been checked by using a DII inhibitor, iopanoic acid, and also by an anti-thyroid drug PTU (propyl thiouracil) that does not inhibit DII. This method can, thus, be a novel and quick indirect method of assaying DII activity of cerebral cortex non-radiometrically.