High-affinity binding of thyroid hormones to neuroblastoma plasma membranes.
The binding of thyroid hormones to isolated plasma membranes was studied in NB41A3 neuroblasts. Saturable binding of L-T3, D-T3 and L-T4 was observed. Binding was time-dependent, with equilibrium reached in less than 60 min and maximal binding occurring between pH 7.4 and 7. Saturation experiments demonstrated two classes of sites for L-T3: a high-affinity site with Ka 8.4 X 10(9) M-1 and a low-affinity site with Ka 7.3 X 10(6) M-1.L-T3 and D-T3 inhibited each other's binding, L-T3 being several-times more potent. Affinity labeling of isolated membranes with bromoacetylated thyroid hormones disclosed stereospecific binding to SDS-PAGE bands with approximate molecular masses of 27 kDa (preferentially labeled by BrAc-L-T3), 32 kDa (preferentially labeled by BrAc-D-T3), and 48 and 87 kDa (preferentially labeled by BrAc-L-T4). Binding of BrAc-L-T3 to the 27 kDa band accounted for 3.4% of total binding, was selectively inhibited by excess L-T3, and may be involved in intracellular transport of L-T3.
Gonçalves
E
E
Clinical Endocrinology Branch, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Lakshmanan
M
M
Cahnmann
H J
HJ
Robbins
J
J
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D008970:Molecular Weight; D009447:Neuroblastoma / Q000378:metabolism*; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*; D014285:Triiodothyronine, Reverse / Q000378:metabolism*
D008565:Membrane Proteins; D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D013974:Thyroxine