[Pregnancy-associated molecular variation of thyroxine-binding globulin in health and in various diseases of man].

A molecular variant of human serum thyroxine-binding globulin (TBG), containing only triantennary oligosaccharide chains and having a more prolonged in vivo survival (TBG-1), was first detected in normal pregnancy and then in the postpartum period. Serum TBG-1 was measured in normal and in some pathological conditions associated with normal or increased TBG biosynthesis using a combination of Con A-Sepharose 4B microcolumn affinity chromatography and a highly sensitive TBG radioimmunoassay. TBG-1 was shown to be present in the sera of healthy subjects (0.21 +/- 0.04 micrograms/ml, n = 60; 1.15% of total TBG). The proportion of TBG-1 in total serum TBG was significantly increased (up to 9.5%) in conditions with serum TBG excess (cancer, hypothyroidism and liver diseases). It has been assumed that a selective enhancement of biosynthesis of the TBG molecular variant with a prolonged half-life in the circulation during the posttranslational modification of the polypeptide chain is a response to the body requirements in a high TBG concentration.