Distribution and Metabolism of I 131 -Labeled Thyroxine and Triiodothyronine in Subcellular Fractions of Chicken Myocardium. ∗ †

Summary

There was no selective concentration of T-4 or T-3 in any of the subcellular fractions of chicken cardiac tissue. Both T-4 and T-3 followed the same pattern of distribution in all fractions except the mitochondria where T-4 was retained to a greater extent than was T-3. The microsomal fraction consistently deiodinated T-3 at a faster rate than occurred with T-4. Neither the mitochondrial nor the supernatant fractions showed appreciable deiodinating ability under the conditions of the experiment.