SERUM PROTEINS AND THYROXINE-PROTEIN INTERACTION IN EARLY HUMAN FETUSES

Abstract

Serum has been examined in 13 human fetuses ranging in size (crown to rump) from 5.8 to 14.3 cm and in age from 8 to 20 weeks. Fetal serum contains a protein fraction moving between albumin and [alpha]1-globulin in barbital buffer and with [alpha]1-globulin in ammonium carbonate. This post-albumin component comprised 29[degree]/o of the total protein in the youngest fetus and decreased with age. It did not contain PAS-positive glyco-proteins, did not bind bromophenol blue prior to denaturation, and exhibited a slight affinity for thyroxine. During fetal development total protein, albumin, and [gamma]-globulin increased. Protein-bound iodine determined in the oldest fetuses was lower than in the adult, ranging from 1. 4 to 1. 6 [mu]g per 100 ml. Zone electrophoresis in barbital, ammonium carbonate, or borate buffer, pH 8. 6, revealed in the fetus the same thyroxine-binding proteins present in the adult: pre-albumin, albumin and inter-[alpha]-globulin (TBG). In starch gel electrophoresis there was a more slowly moving band of thyroxine which was absent in the adult and corresponded to the large amount of thyroxine found by reverse-flow electrophoresis in albumin (barbital) or in prealbumin (ammonium carbonate). This phenomenon was inversely related to the amount of TBG-bound thyroxine and appears to represent thyroxine dissociated from protein during electrophoresis. Quantitative studies indicated that thyroxine binding by TBG in fetal serum was low, compared with the adult, and increased with fetal size.