Entropy protein transition

In addition to chemical reactions, the isokinetic relationship can be applied to various physical processes accompanied by enthalpy change. Correlations of this kind were found between enthalpies and entropies of solution (20, 83-92), vaporization (86, 91), sublimation (93, 94), desorption (95), and diffusion (96, 97) and between the two parameters characterizing the temperature dependence of thermochromic transitions (98). A kind of isokinetic relationship was claimed even for enthalpy and entropy of pure substances when relative values referred to those at 298° K are used (99). Enthalpies and entropies of intermolecular interaction were correlated for solutions, pure liquids, and crystals (6). Quite generally, for any temperature-dependent physical quantity, the activation parameters can be computed in a formal way, and correlations between them have been observed for dielectric absorption (100) and resistance of semiconductors (101-105) or fluidity (40, 106). On the other hand, the isokinetic relationship seems to hold in reactions of widely different kinds, starting from elementary processes in the gas phase (107) and including recombination reactions in the solid phase (108), polymerization reactions (109), and inorganic complex formation (110-112), up to such biochemical reactions as denaturation of proteins (113) and even such biological processes as hemolysis of erythrocytes (114). 

A suitable model for the oxygen carrier protein hemerythrin is [Fe2(Et-HPTB)(OBz)](BF4)2 (Et-HPTB = AWAT,iV -tetrakis[(N-ethyl-2-benzimidazolyl)methyl]-2-hydroxy-l,3-diaminopropane, OBz = benzoate). It can mimic the formation of a binuclear peroxo iron complex in the natural system (101). The measured value of -12.8 cm3 mol1 for the activation volume of the oxidation reaction together with the negative value of the activation entropy confirm the highly structured nature of the transition state. 

The van t Hoff plots for thermal denaturation of proteins are linear in the transition region, thus allowing the enthalpy change (AHm) of unfolding at the transition temperature (Tm) to be estimated. Because of the change in free energy in (AG) = 0 at Tm (reversible process), the entropy of unfolding (ASm) at the transition midpoint can be calculated from ... 

MICHAELIS-MENTEN KINETICS PREEXPONENTIAL FACTOR ARRHENIUS EQUATION COLLISION THEORY TRANSITION-STATE THEORY ENTROPY OF ACTIVATION PRENYL-PROTEIN-SPECIFIC ENDOPEP-TIDASE... 

Thermodynamics of Proteins Calculating the Entropy of a Helix-Coil Transition in a Small Antibacterial Peptide using Statistical Mechanics (J. Mol. Bio. 1999, 294, 785-794. "Thermodynamics of the a-Helix-Coil Transition of Amphipathic Peptides in a Membrane Environment Implications for the Peptide-Membrane Binding Equilibrium")... 

The specific enthalpy and entropy of the conformation transition of proteins from the native to denatured state has an upper limit that is reached above 140°C and seems to be universal for all compact globular proteins (Figs. 4 and S). By enthalpy and entropy of conformational tran-... 

For compact proteins with molecular masses of greater than 10,000 and saturation of native structure by intramolecular hydrogen bonds of about 0.75 0.10 mole of bonds per mole of amino acid residues, the asymptotic values of enthalpy and entropy of the conformational transition, calculated per amino acid residue, amount to A%H(TX) = (6.25 0.2) kJ mol-1 and A 5(7 x) = (17.6 0.6) J K-1 mol-1. For some noncompact proteins (e.g., histones) or small globular proteins with molecular masses... 

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