Thyroxine binding to members and non-members of the serine protease inhibitor family.
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 [125I]T4 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.
Benvenga
S
S
Department of Clinical and Experimental Medicine and Pharmacology, University of Messina School of Medicine, Italy. s.benvenga@me.nettuno.it
Lapa
D
D
Trimarchi
F
F
D000328:Adult; D004586:Electrophoresis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011228:Prealbumin / Q000378:metabolism; D011233:Precipitin Tests; D015842:Serine Proteinase Inhibitors / Q000378:metabolism*; D012709:Serum Albumin / Q000378:metabolism; D013974:Thyroxine / Q000378:metabolism*; D013975:Thyroxine-Binding Proteins / Q000378:metabolism
D011228:Prealbumin; D015842:Serine Proteinase Inhibitors; D012709:Serum Albumin; D013975:Thyroxine-Binding Proteins; D013974:Thyroxine