Kinetic analysis of the uptake of thyroid hormones by the human erythrocyte.
The uptake of 3,5,3'-tri-iodothyronine (T3) by human erythrocytes was shown to occur by two saturable processes. System I (Michaelis constant (Km) = 109 +/- 40 (mean +/- S.D.) nmol/l; maximal velocity (Vmax) = 43 +/- 16 pmol/min per 10(9) cells) was observed over the range 1-50 nmol T3/l whilst system II (Km = 8.8 +/- 8.0 pmol/l; Vmax = 29 +/- 6 fmol/min per 10(9) cells) was observed over the range 1-500 pmol T3/l. At low concentrations (1-500 pmol/l) uptake processes equivalent to system II could be demonstrated for thyroxine and 3,3',5'-tri-iodothyronine also. System II had the properties of a carrier-mediated process.
Ball
S G
SG
Department of Medicine, University of Birmingham, Queen Elizabeth Hospital.
Ramsden
D B
DB
D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007700:Kinetics; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D014285:Triiodothyronine, Reverse / Q000097:blood
D007457:Iodine Radioisotopes; D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D013974:Thyroxine