Thermodynamic analysis of the interaction of prolactin with its receptor in the rabbit mammary-gland microsomes.
The interaction of prolactin (PRL) with its membrane receptor depends markedly on temperature. Thermodynamic parameters for this reaction have been evaluated from data for time-course kinetics and equilibrium binding at multiple temperatures between 19 and 31 degrees C. The free-energy change with temperature and the van't Hoff plot were found to be linear. These suggest that there are minimal structure changes at the PRL-receptor contact site over this temperature range. The positive signs of the entropy and enthalpy of reaction, and of the entropy of activation (delta S++) for association, indicate that the hydrophobic bonding is the most significant force involved in PRL-receptor formation. The delta S++ for dissociation was negative, and the enthalpy of activation for dissociation was about 20.3 kJ.mol-1 larger than that for association, indicating that the PRL-receptor complex is further stabilized by contributions of hydrogen bonds and van der Waals contacts after the initial interaction. The free energy of activation for dissociation, at 25 degrees C was about 2.5-fold larger than that for association. This would cause slow dissociation of PRL from its receptor.
Sakai
S
S
Department of Animal Breeding, Faculty of Agriculture, University of Tokyo, Japan.
Suzuki
M
M
Kohmoto
K
K
D000818:Animals; D005260:Female; D007457:Iodine Radioisotopes; D007700:Kinetics; D008321:Mammary Glands, Animal / Q000378:metabolism / Q000648:ultrastructure*; D008861:Microsomes / Q000378:metabolism / Q000648:ultrastructure*; D011388:Prolactin / Q000378:metabolism*; D011817:Rabbits; D011981:Receptors, Prolactin / Q000378:metabolism*; D012756:Sheep; D013696:Temperature; D013816:Thermodynamics
D007457:Iodine Radioisotopes; D011981:Receptors, Prolactin; D011388:Prolactin