Kinetic analysis of the uptake of thyroid hormones by the human erythrocyte

Abstract

ABSTRACT 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 109 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 109 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. Journal of Endocrinology (1989) 123, 143–148