Regulation of thyroid hormone binding to its cytosolic binding protein by L-α-alanine

Abstract

The human cytosolic thyroid hormone binding protein (p58) was recently shown to be a monomer of pyruvate kinase, subtype PKM 2, and have intrinsic pyruvate kinase activity. The present study evaluated the effect of L-α-alanine on the binding of 3,3′,5-triiodo-L-thyronine (T 3) and enzymatic activity of p58. Analysis of the competitive binding data indicated that alanine, at the physiological concentration, is a non-competitive inhibitor of T 3 binding to p58. Furthermore, alanine was found to be a “mixed” inhibitor of the substrate phosphoenol pyruvate. However, binding of alanine to p58 did not block the association of p58 to form the tetrameric pyruvate kinase.