Retinoic acid inhibition of thyroxine binding to human transthyretin.
All-trans retinoic acid is a potent inhibitor of [125I]-thyroxine (T4) binding to human erythrocyte membranes and can block the activation by thyroid hormone of erythrocyte Ca(2+)-ATPase [J. Biol. Chem. (1989) 264, 687-689]. In the present studies, retinoic acid was examined for its ability to displace thyroxine from binding sites on human transthyretin (TTR). Scatchard analysis of [125I]T4 binding to purified TTR, determined by equilibrium dialysis, revealed two classes of binding sites with association constants of 3.2 x 10(9) M-1 and 8.1 x 10(6) M-1. All-trans retinoic acid also displaced [125I]T4; 40% of the specifically bound [125I]T4 was displaced at a retinoic acid concentration of 2 x 10(-5) M. Analysis of the high affinity T4 binding site suggests that the Ka for retinoic acid to that site is approx. 10(7) M-1. 8-Anilinonaphthalene-1-sulfonate (ANS), a strongly fluorescing dye, binds to the thyroxine binding sites on TTR. T4 and 3,5,3'-L-triiodothyronine (T3) shifted the fluorescence emission maximum and intensity of an ANS-TTR solution toward the spectrum obtained from uncomplexed ANS. All-trans retinoic acid caused a similar shift in the emission spectrum of ANS, but was less potent than T4. Retinol failed to quench the emission intensity of the ANS-TTR complex, while 13-cis-retinoic acid was less effective than all-trans retinoic acid.
Smith
T J
TJ
Department of Medicine, Albany Medical College, NY 12208.
Davis
F B
FB
Deziel
M R
MR
Davis
P J
PJ
Ramsden
D B
DB
Schoenl
M
M
D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D001665:Binding Sites; D005456:Fluorescent Dyes; D006801:Humans; D007457:Iodine Radioisotopes; D011228:Prealbumin / Q000737:chemistry* / Q000494:pharmacology; D013974:Thyroxine / Q000737:chemistry* / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology*
D000817:Anilino Naphthalenesulfonates; D005456:Fluorescent Dyes; D007457:Iodine Radioisotopes; D011228:Prealbumin; D014212:Tretinoin; C027132:1-anilino-8-naphthalenesulfonate; D013974:Thyroxine