Interaction Between Prolactin and Rabbit Mammary Prolactin Receptor in the Presence of Environment-Modifying Agents.

Suzuki

Kohmoto

1990

Biochemical Journal

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 '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 (AST) for association, indicate that the hydrophobic bonding is the most significant force involved in PRL-receptor formation. The AS-for dissociation was negative, and the enthalpy of activation for dissociation was about 20.3 kJ mol-' 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 'C, was about 2.5-fold larger than that for association. This would cause slow dissociation of PRL from its receptor.

Section: Free Energy Enthalpy Entropy Of Prl-receptor Reactionsupporting

confidence: 86%

Section: Free Energy Enthalpy Entropy Of Prl-receptor Reactionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Thermodynamic analysis of the interaction of prolactin with its receptor in the rabbit mammary-gland microsomes

Suzuki

Kohmoto

1990

Biochemical Journal

“…Our previous results suggested that the PRL-receptor complex is further stabilized by the contributions of hydrogen bonds and probably van der Waals contacts after the hydrophobic interaction (Sakai & Suzuki, 1988;Sakai et al, 1990). It is expected that the PRL-receptor complex becomes less stable as the incubation temperature is increased.…”

Section: Discussionmentioning

confidence: 96%

Effect of hormones on dissociation of prolactin from the rabbit mammary gland prolactin receptor

1991

Biochemical Journal

Using microsomes prepared from rabbit mammary gland, the dissociation of prolactin (PRL) from its receptor was determined in the presence of peptide hormones or various concentrations of PRL. Among the hormones tested, PRL (ovine, mouse and bullfrog), human growth hormone and human placental lactogen each accelerated the dissociation of PRL in a manner proportional to their receptor-binding activities. Hormone-dependent dissociation was observed at higher concentrations than those at which the binding of PRL was completely inhibited by lactogenic hormones. In the concentration range 0.1 ng/ml-10 micrograms/ml, PRL increased the rate of dissociation in a logarithmic concentration-dependent manner. It was concluded that the dissociation of PRL from its receptor caused by lactogenic hormones is dependent on the hormone concentration. Arrhenius plot analysis revealed that PRL changed the frequency factor for the dissociation reaction. PRL in the medium inhibited the re-association of dissociated PRL. The data also suggested that PRL regulates the rate of dissociation by interacting with the PRL-receptor complex.

“…At high concentrations, the k+1 decreased greatly, in the presence of bivalent cations. This is probably due to the alteration of the reaction environment (Sakai and Suzuki, 1989). Both Ca2+ and Mg2+ ions at high concentrations are known to have a chaotropic action.…”

mentioning

confidence: 99%

Mechanism of Biphasic Action of Mono- and Bivalent Salts on the Binding of Prolactin to the Receptor in the Rabbits Mammary Gland.

Khomoto

1989

Endocrinol Japon

Self Cite

The influence of NaCl, KCl, CaCl2, and MgCl2 on the binding of prolactin (PRL) to its receptor was investigated. The salts were dissolved in a metallic ion-free binding buffer and had biphasic effects on changes in the association rate constant (k+1) of PRL binding, depending on their concentrations:there was an increase in the k+1 at lower concentrations and a decrease at higher concentrations.The dissociation rate of bound PRL was unaffected. NaCl at any concentration did not change the binding capacity. Bivalent salts, at higher than 25mM, increased the capacity about 1.6-fold as compared to the 0mM control.By cross-linking the PRL-receptor complex, the band of a molecular weight (Mr) 34,500 receptor could always be detected on the autoradiogram.An Mr 78,000 receptor appeared only after incubation with bivalent salts. Data indicate that the binding of PRL to an Mr 78,000 receptor is directly regulated by bivalent cation.