Rates of dissociation of steroid and thyroid hormones from human serum albumin.
A rapid filtration assay employing dextran-coated charcoal as acceptor particles for free hormone was used to measure rates of dissociation of steroid and thyroid hormones from human serum albumin. Modification of a previously described assay allowed measurements at 1-s intervals. Nevertheless, this still permitted only minimum estimates of the dissociation rate constants. The hormones studied were thyroxine, 3,5,3'-triiodothyronine, cortisol, corticosterone, testosterone, dihydrotestosterone, estradiol, progesterone, and aldosterone. The apparent dissociation rate constant of the thyroxine-albumin complex at 37 degrees C was 1.3 +/- 0.2 s-1 (t 1/2, 0.5 s). The apparent dissociation rate constants of the other hormone-albumin complexes at 37 degrees C generally exceeded 2 s-1 (t 1/2 less than 0.35 s). Apparent dissociation rate constants at 4 degrees C were only slightly lower. These findings indicate that steroid and thyroid hormones dissociate from albumin rapidly compared with the 1-s capillary transit times that characterize many tissues.
Mendel
C M
CM
Cardiovascular Research Institute, University of California, San Francisco 94143-0130.
Miller
M B
MB
Siiteri
P K
PK
Murai
J T
JT
D000450:Aldosterone / Q000097:blood; D003345:Corticosterone / Q000097:blood; D013196:Dihydrotestosterone / Q000097:blood; D004958:Estradiol / Q000097:blood; D006854:Hydrocortisone / Q000097:blood; D007700:Kinetics; D011374:Progesterone / Q000097:blood; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism*; D013256:Steroids / Q000097:blood*; D013739:Testosterone / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D014316:Tritium
D012709:Serum Albumin; D013256:Steroids; D014284:Triiodothyronine; D013196:Dihydrotestosterone; D014316:Tritium; D013739:Testosterone; D000450:Aldosterone; D011374:Progesterone; D004958:Estradiol; D013974:Thyroxine; D003345:Corticosterone; D006854:Hydrocortisone