Proteins thermodynamic stability

The decrease of protein thermodynamic stability on pH decreasing suggests a preferential binding of protons to the unfolded state. The effect of pH on the standard denaturation Gibbs function, tyfi, has been theoretically analyzed by... 

The thermodynamic stability of a protein in its native state is small and depends on the differences in entropy and enthalpy between the native state and the unfolded state. From the biological point of view it is important that this free energy difference is small because cells must be able to degrade proteins as well as synthesize them, and the functions of many proteins require structural flexibility. 

The extremely important feature of proteins is their idiosyncratic folds. When describing proteins the problem of all their folds is not solved just by the thermodynamic stability of the interactions between the amino acids much though this may be approximately true if we take the majority of proteins (see Lesk in Further Reading). 

L. Zheng and J.D. Brennan, Measurement of intrinsic fluorescence to probe the conformational flexibility and thermodynamic stability of a single tryptophan protein entrapped in a sol-gel derived glass matrix. Analyst 123, 1735-1744 (1998). 

Solution equilibria for gadolinium imaging agents have been studied with consideration for pharmacokinetic, protein binding, elimination, and safety aspects of the dmgs. The thermodynamic stability constant, Kq defined by equation 7.4 must be large for clinically viable agents. Some Kq l data are listed in Table 7.3. 

As seen above (equation (5)), the basis of the simple bioaccumulation models is that the metal forms a complex with a carrier or channel protein at the surface of the biological membrane prior to internalisation. In the case of trace metals, it is extremely difficult to determine thermodynamic stability or kinetic rate constants for the adsorption, since for living cells it is nearly impossible to experimentally isolate adsorption to the membrane internalisation sites (equation (3)) from the other processes occurring simultaneously (e.g. mass transport complexation adsorption to other nonspecific sites, Seen, (equation (31)) internalisation). 

Poklar, N., N. Petrovcic, M. Oblak, and G. Vesnaver. 1999. Thermodynamic stability of ribonuclease A in alkylurea solutions and preferential solvation changes accompanying its thermal denaturation a calorimetric and spectroscopic study. Protein Sci 8 832-840. 

Powell, K.D. Wales, T.E. Fitzgerald, M.C. Thermodynamic stability measurements on multimeric proteins using a new H/D exchange-and matrix-assisted laser desorption/ ionization (MALDl) mass spectrometry-based method. Protein Sci. 2002, 11, 841-851. 

Formalisms to relate the observed rates of amide hydrogen exchange to thermodynamic stabilization of proteins have been developed [38]. Amide hydrogens of proteins in the native, folded state are proposed to exchange according to the following equation ... 

The thermodynamic stability of hemopexin has been examined using DSC (Fig. 13), which showed apo-hemopexin to be a stable protein with a single Tm of 54°C (AH 185 kcal/mol), which increases to 66.5°C (AH 290 kcal/mol) upon binding heme (130). The N-domain of hemopexin is less stable (Tm 52°C, AH 95 kcal/mol) but is even more strikingly stabilized by ferri-heme (T 78°C, AH 370 kcal/mol). The presence of C-domain (Tii 49.5°C, AH 140 kcal/mol) slightly destabilizes heme-N-domain (Tm 75°C, AH 320 kcal/mol) (130), showing another effect of interdomain interactions that may act in heme release. 

In contrast to their instability free in solution, flavin semiquinones bound to proteins are generally (although there are exceptions) quite stable and can be generated in nearly quantitative yields. This stability results from thermodynamic considerations in which the oxidized/semiquinone oxidation-reduction couple is usually more positive and well separated from the semiquinone/hydroquinone couple. In addition to thermodynamic stabilization, kinetic stabilization of protein-bound semiquinones has also been observed and will be discussed in more detail in subsequent portions of this article. 

Thermodynamic stability is not evenly distributed over the structure of a protein—the molecule has regions of high and low stability. For example, a protein... 

Two-State Model Thermodynamic Stability of Proteins (Unfolding) I 491... 

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