Ternary complex model thermodynamic

While the extended ternary complex model accounts for the presence of constitutive receptor activity in the absence of ligands, it is thermodynamically incomplete from the standpoint of the interaction of receptor and G-protein species. Specifically, it must be possible from a thermodynamic point of view for the inactive state receptor (ligand bound and unbound) to interact with G-proteins. The cubic ternary complex model accommodates this possibility [23-25]. From a practical point of view, it allows for the potential of receptors (whether unbound or bound by inverse agonists) to sequester G-proteins into a nonsignaling state. 

The simple ternary complex model (Fig. 2A) describes the binding of ligands to GPCRs, leading to the activation of G protein (De Lean et ah, 1980 Lefkowitz et at, 1993). This model is based on the four equilibrium reactions that account for all of the thermodynamically possible interactions between the three species ligand, GPCR, and G protein. 

Since it is known that different areas of the cytosolic loops of receptors activate different G proteins [191], it is evident that agonists can stabilize multiple active receptor conformations, thus changing not only the degree, but also the quality of receptor activation [192]. Consequently, three-state to multistate models have been developed. Furthermore, in thermodynamic terms must be a provision for the inactive receptor to also interact with G proteins, which lead to a more complex model for GPCRs, named the cubic ternary complex model [193]. Taking into account the concomitant binding of an orthosteric ligand led to a thermodynamically complete, extended model, named the quaternary complex model [194]. The above mentioned and additional models have been recently reviewed by Maudsley et al. [192], Kenakin et al. [195] and Christopoulos et al. [196]. Therein, the potential for allosteric... 

Although the ETC model explains most GPCR behavior, a more thermodynamically complete model, the cubic ternary complex (CTC) model (Fig. 6), was subsequently proposed (68-70). This model is merely an extension of the ETC model (that is, the ETC model is one of the subsets making up the CTC model) that allows for the existence of an inactive ternary complex, ARG, although both models similarly predict GPCR behavior. However, at the time of development of the ETC and CTC models, neither specifically accommodated experimental... 

It can be seen from this equation that maximal constitutive activity need not reach a maximal asymptote of unity. Submaximal constitutive activity has been observed with some receptors with maximal receptor expression [26]. While there is scattered evidence that the cubic ternary complex is operative in some receptor systems, and while it is thermodynamically more complete, it also is heuristic in that there are more individually nonverifiable constants than other models. This makes this model limited in practical application. 

It has already been noticed (see 3.9.4) that according to the mentioned concepts several ternary compounds may be considered as the result of a sort of structural interaction between binary compounds. As a consequence some regular trend could also be predicted for their occurrence in their phase diagrams and in the description (and perhaps modelling) of their thermodynamic properties. A few details about this type of structural relationships will be considered in the following and, in this introduction, examples of blocks of simple structural types and of their combination in more complex types will be described. 

The present paper gives an overview of results on high-pressure phase equilibria in the ternary system carbon dioxide-water-1-propanol, which has been investigated at temperatures between 288 and 333 K and pressures up to 16 MPa. Furthermore, pressure-temperature data on critical lines, which bound the region where multiphase equilibria are oberserved were taken. This study continues the series of previous investigations on ternary systems with the polar solvents acetone [2], isopropanol [3] and propionic add [4], A classification of the different types of phase behaviour and thermodynamic methods to model the complex phase behaviour with cubic equations of state are discussed. 

The full extent and variety of the phase behavior for water-isopropanol-C02 mixtures observed experimentally and calculated with the Peng-Robinson equation of state was not anticipated based on known phase behavior for the constituent binary mixtures or similar ternary mixtures. These results suggest that multiphase behavior for related model surfactant systems could also be complex. Measurements of all the critical endpoint curves, the tricritical points, and secondary critical endpoint for such systems would be tedious and are extremely difficult. However, by coupling limited experimental data with a thermodynamic model based on this cubic equation of state, complex multiphase behavior can be comprehensively described. 

A reasonable thermodynamic model was tried to explain the effect of fluoride concentration on the MgO solubility in the MgCl2-NaCl-NaF ternary melts. However, both the activity model used to calculate the activity of MgCl2 and MgF2 and the understanding of the Mg-O-Cl(F) complexes formed in the melt seemed to be too simple to give a reasonable mechanism for MgO solubility in these complicated melts. 

The thermodynamic model of Felmy et al. [1997FEL/RAI], [1999FEL/RAI] is based on Pitzer s ion interaction approach including binary and ternary parameters for the complex Th(C03)5 cf.. Appendix A review of [1997FEL/RAI]). Accordingly, the value of logj X°j 5 is not directly comparable to that of [19940ST/BRU]. 

Fuger (1979) and Fuger et al. (1983) reviewed experimental thermodynamic data on complex halides of the f elements, almost all of which were limited to ternary An chlorides. Jenkins and Pratt (1979) used an ionic model for lattice-energy calculation to place the energetics of formation of complex halides of d and f transition elements (from binary halides)... 

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