Isoelectric focussing of human thyroxine binding globulin (thyropexin) and human prealbumin (transthyretin).

Two batches of the highly purified thyroid hormone-binding plasma proteins, human thyropexin and transthyretin, which were prepared in gram quantities for use in animal experiments, were subjected to analysis by isoelectric focussing. Under these conditions, it was observed that human transthyretin was composed of two components. This was presumably due to the use of 8 mol/l urea. The preparations of both human transthyretin and human thyropexin contained some products of decomposition which probably arose in the course of the purification processes and, in addition, possibly also contained some normal genetic variants of human thyropexin. In spite of the alterations, both protein preparations largely retained their thyroid hormone-binding capacity, which is essential for in vivo studies on the re-entry of thyroid hormones from the extravascular space into the circulation. For therapeutic use in thyrotoxicosis, human transthyretin seems to be preferable to human thyropexin.