Inverse temperature transitions hydrophobic effect

Figure 5.10. An embodiment of the comprehensive hydrophobic effect in terms of a plot of the temperature for the onset of phase separation for hydrophobic association, Tb, versus AGha. the Gibbs free energy of hydrophobic association for the amino acid residues, calculated by means of Equation (5.10b) using the heats of the phase (inverse temperature) transition (AH,). Values were taken from Table 5.3. Tb and T, were determined from the onset of the phase separation as defined in Figure 5.1C,B, respectively. The estimates of AGha utilized the AH, data listed in Table 5.1 for fx = 0.2 but extrapolated to fx = 1, and the Gly (G) residue was taken as the...

Early in our studies it was expected that the post-translational modification of proline hydroxylation, so important to proper collagen structure and function, would raise the value of the temperature, T, for the onset of the inverse temperature transition for models of elastin. Accordingly, hydroxyproline (Hyp) was incorporated by chemical synthesis into the basic repeating sequence to give the protein-based polymers poly[fvs,i(Val-Pro-Gly-Val-Gly), fHyp( al-Hyp-Gly-Val-Gly)], where f sl -i- fnyp = 1 and values of fnyp were 0, 0.01, and 0.1. The effect of prolyl hydroxylation is shown in Figure 7.49. Replacement of proline by hydroxyproline markedly raises the temperature for hydrophobic association. Prolyl hydroxylation moves the movable cusp of... 

Figuke 7.49. Effect of prolyl hydroxylation on hydrophobic association (insolubility). Temperature profiles show turbidity formation due to the aggregation attending the onset of the inverse temperature transition. The value for the onset temperature is taken at 50% of the maximal turbidity and is called T,. Hydroxylation markedly shifts the polymer to solubility. (Reproduced with permission from Urry et al. )... 

Net Heat Changes for the Inverse Temperature Transitions of the Comprehensive Hydrophobic Effect Are Endothermic Due to the Conversion of Hydrophobic Hydration to Bulk Water ... 

As reviewed in Chapter 7 with a focus on the issue of insolubility, extensive phenomenological correlations exist between muscle contraction and contraction by model proteins capable of inverse temperature transitions of hydrophobic association. As we proceed to examination of muscle contraction at the molecular level, a brief restatement of those correlations follows with observations of rigor at the gross anatomical level and with related physiological phenomena at the myofibril level. Each of the phenomena, seen in the elastic-contractile model proteins as an integral part of the comprehensive hydrophobic effect, reappear in the properties and behavior of muscle. More complete descriptions with references are given in Chapter 7, sections 7.2.2, and 7.2.3. 

In Chapter 5, based on an inverse temperature transition due to hydrophobic association in water, a set of Axioms were derived from the phenomenological demonstration that de novo designed model proteins could efficiently interconvert the set of energies interconverted by living organisms. Then there followed a series of experimental results and analyses that defined the comprehensive hydrophobic effect. 

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