L-Triiodothyronine Binding to Serum Protein. I. Competition by Thyronine. ∗ †

Abstract

Summary

1, It has been shown that DL-thyronine competes for the binding sites in human serum proteins of both T-3 and T-4 to the extent of 12-18% for the former and 4-7% for the latter. 2. It thus appears that thyroxine is more firmly held to these proteins than T-3; or that T-O is more like T-3 than like T-4 in its binding properties. 3. 3,5-diiodo-3'-isopropyl-thyronine was also shown to be a competitor of T-3 for binding sites of serum proteins, although to a much lower extent (2-5%). Monoiodo and Diiodo-tyrosine did not show competition for these binding sites.