THYROXINE-BINDING CAPACITY OF SERUM IN NORMAL MAN 1

Abstract

The thyroxine-binding capacity of the specific thyroxine-binding protein (TBP) in normal serum was studied by the use of thyroxine labeled with I131, and zone electrophoresis at pH 8.6. It was shown that thyroxine added to serum exchanges readily with the endogenous serum thyroxine with regard to protein binding. The TBP was shown to have a limited capacity to bind thyroxine, but the measurement of the actual binding capacity was complicated by the fact that excess thyroxine is bound to other serum proteins, notably to albumin, and the fact that the TBP could not be isolated from the other alpha globulins, It appears likely, however, that saturation of TBP occurs at serum thyroxine levels at least 2 to 3 times normal.