Thyroxine binding to members and non-members of the serine protease inhibitor family.

摘要

Partition of T4 to plasma proteins is classically attributed only to TBGC approximately/= 70), transthyretin (approximately/= 15) and albumin (approximately/= 10), based on zone electrophoresis. Since TBG migration spans the alpha1 and alpha2 regions, and since HDL, which have alpha1 migration, transport approximately/= 4 of circulating T4, other alpha-globulins could bind T4 and "contaminate" the TBG area. Hence, we determined the association of 125IT4 to TBG and, for comparison, to transthyretin and albumin. Sera from 50 normolipidemic individuals were equilibrated with 125I T4 and analyzed by both zone electrophoresis and radioimmunoprecipitation with specific antisera. Transthyretin-T4 or albumin-T4 bindings as assessed by the two methods agreed, while TBG-T4 did not, because other alpha-globulins carrying T4 with low affinity co-migrated with TBG. Some, but not all, of these alpha-globulins belong to the same superfamily of TBG and also bind steroid hormones.