Specific Receptors for Thyroxine in Nuclear Non-Historie Proteins of Rat Thymus during Early, Medium and Late Period of Life

Summary

Specific binding of ¹²⁵I-thyroxine to thymus nuclear non-histone proteins of rats aged 7, 14, 45, 80 and 365 days was studied. In 0.4 mol l⁻¹ NaCl nuclear extract of thymocytes practically the same values of K_a were found in rats aged 7, 14, 45 and 80 days (5.72 ± 0.11 x10⁹ l mol⁻¹, 3.44 ± 1.65x10⁹ lmol⁻¹, 5.00 ± 1.09x 1⁹1 mol⁻¹ and 5.55 ± 0.95x10⁹ lmol⁻¹, respectively). As compared to groups of animals of 7, 45 and 80 days of age a marked diminution of K_a (== 1.30 ± 0.25X10⁹1 mol⁻¹) with P < 0.001, < 0.02 and < 0.01, respectively, was found in rats aged 365 days. The highest value representing maximum binding capacity (MBC) of ¹²⁵I-thyroxine was noted in rats aged 45 days (MBC = 6.16 ± 0.58 X10¹⁰ molecules per mg of protein) and in adult rats (80 days old) (MBC = 5.82 ± 1.28x10¹⁰ molecules mg⁻¹). In rats aged 7 days a lower value for MBC (= 1.92 ± 0.77 X10¹⁰ molecules mg-¹; P < 0.01) was observed as compared to the animals aged 45 days (see above). Similar decrease was found also in old rats aged 365 days (MBC = 3.46 ± 0.69X10¹⁰ molecules mg⁻¹; P < 0.02).

The data quantify the affinity and the specific ¹²⁵I-thyroxine binding capacity in nuclear non-histone proteins of rat thymus during early, adult and late period of life.

Key Words

Thyroxine receptor - Thymus - Development