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

Abstract

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.

Complexation between carrageenan and methylene blue for sensor design

“…Van't Hoff plot demonstrated linear regression (R 2 =0.982) as the enthalpy change (ΔH) is constant throughout the test conducted at temperature range of 298-323 K. Additionally, linear plot suggested that the structure of binding site of carrageenans does not have significant change in that temperature range tested [19]. Negative value of ΔH (-18.54 kJ mol -1 ) described that the MB-Iota-carrageenan complexation is an exothermic process.…”

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

“…Microsomes were prepared from mid-lactating rabbit mammary glands. The protocol for the PRL-binding assay has been described previously (Sakai et al, 1990). In the present investigation the concentrations of microsomes and 1251.…”

“…where R and Tare the gas constant and the absolute temperature respectively. The free energy of activation (AG:), enthalpy of activation (AHP) and entropy of activation (AST) for dissociation were calculated according to transition state theory (Sakai et al, 1990). All thermodynamic data were standardized at 25 'C.…”

“…The interaction of PRL with its receptor has been evaluated by thermodynamic analysis (Haro & Talamantes, 1985;Sakai et al, 1990). We showed that PRL forms a very stable complex with the rabbit mammary gland PRL receptor (Sakai et al, 1990), and the rate of PRL dissociation from its receptor is low (Kelly et al, 1980).…”

“…The interaction of PRL with its receptor has been evaluated by thermodynamic analysis (Haro & Talamantes, 1985;Sakai et al, 1990). We showed that PRL forms a very stable complex with the rabbit mammary gland PRL receptor (Sakai et al, 1990), and the rate of PRL dissociation from its receptor is low (Kelly et al, 1980). However, it is also known that the presence of PRL during the dissociation reaction increases the rate of PRL dissociation above that which is observed in its absence (Perry & Jacobs, 1978;Shiu, 1979;Haro & Talamantes, 1986).…”