Further studies on the temperature dependence of the binding of testosterone to human pregnancy plasma proteins

The binding of testosterone by pregnancy plasma proteins has been studied by a new equilibrium dialysis system. The temperature dependence on the association constant has been investigated and the enthalpy change ΔH and entropy change ΔS have been calculated. By a computer optimization program, the binding constant of the high affinity testosterone binding protein has been estimated from Scatchard plots. The binding reactions were carried out at 5°, 25° and 37° C. The corresponding values were 3.1.10 1.2.10 9 and 7.2.10 8 liter/mole. The resulting enthalpy and entropy changes were −2.0 kcal/mole and 35.0 cal/(mole.degree) respectively. It can be concluded that the binding of testosterone to the specific binding protein is an exothermic reaction and is stabilized by hydrophobic binding forces.