Thyroxine-binding Protein in the Serum of Rabbit Fœtuses

Abstract

HUMAN serum contains a thyroxine-binding protein which moves to a position between the α₁ and α₂ globulins on paper electrophoresis in a barbiturate buffer¹. We have investigated the thyroxine-binding power of maternal and fœtal serum taken from pregnant rabbits at different stages of pregnancy. L-Thyroxine, labelled with iodine-131 and having a specific activity of 5 µc./µgm., was added to samples of the serum to give a concentration of about 0.05 µc./ml. of serum. Half to one hour later, 0.02 ml. of the serum was put on to a strip of Whatman No. 3 MM filter paper and electrophoresis carried out as described elsewhere², using a barbiturate buffer at pH. 8.6 and ionic strength 0.1. After the current had been passed for 18 hr. the papers were dried and the position of the radioactivity determined by means of a continuously recording scanner. The bands of protein on the paper were then stained with lissamine green.