The rates of release and binding of thyroxine by bovine serum.

1. Estimates have been made of the rates of release and binding of thyroxine by bovine serum proteins. The method involves measuring the rates at which columns of Amberlite resin take up thyroxine from serum.2. At 37 degrees C the dissociation rate (the rate of release of bound thyroxine into free solution) is about 2.2% sec(-1).3. The binding of thyroxine by serum is a complex process, the majority of the hormone being ;loosely' bound within 0.1 sec but the over-all process taking some 20 sec to completion.4. A mechanism is proposed for the uptake of thyroxine by the liver. It involves a simple competition between the plasma and the liver binding sites for the free thyroxine released into solution by the dissociation reaction.