Transitions protein temperature

These spectra, taken at variable temperatures and a small polarizing applied magnetic field, show a temperature-dependent transition for spinach ferredoxin. As the temperature is lowered, the effects of an internal magnetic field on the Mossbauer spectra become more distinct until they result at around 30 °K, in a spectrum which is characteristic of the low temperature data of the plant-type ferredoxins (Fig. 11). We attribute this transition in the spectra to spin-lattice relaxation effects. This conclusion is preferred over a spin-spin mechanism as the transition was identical for both the lyophilized and 10 mM aqueous solution samples. Thus, the variable temperature data for reduced spinach ferredoxin indicate that the electron-spin relaxation time is around 10-7 seconds at 50 °K. The temperature at which this transition in the Mossbauer spectra is half-complete is estimated to be the following spinach ferredoxin, 50 K parsley ferredoxin, 60 °K adrenodoxin, putidaredoxin, Clostridium. and Axotobacter iron-sulfur proteins, 100 °K. 

DSC has been used to study the individual protein components of biological membranes of relatively simply protein composition and the interaction of several of these components with lipids and with other proteins. The red blood cell membrane, which has been most intensively studied, exhibits five discrete protein transitions, each of which has been assigned to a specific membrane protein. The response of each of these thermal transitions to variations in temperature and pH as well as to treatment with proteases, phospholipases, specific labelling reagents, and modifiers and inhibitors of selected membrane activities, has provided much useful information on the interactions and functions of these components in the intact erythrocyte membrane (46-49). Similar approaches have been applied to the bovine rod outer segment membrane (50) and to the spinach chloroplast thylakoid membrane (51). 

At present the origin of the new higher-temperature glass-transition that occurred in the polyurethane modules after four weeks in vivo is unknown. Calcium phosphate precipitates and biofilms with high protein density have been observed on orthodontic modules after three weeks in vivo [52], and some diffusion of ion species from salivary fluid into the polymer matrix of the polyurethane modules would be expected. Further DSC study of clinically used orthodontic modules is needed to determine the origins of the new higher-temperature glass-transition and the associated endothermic peak. 

A low-tcmpcraturc, dynamically driven structural transition observed in a polypeptide by solid-state NMR spectroscopy has been reported by Bajaj et At low temperatures, proteins and other biomolecules are generally found to exhibit dynamic as well as structural transitions. This includes a so-called protein glass transition that is universally observed in systems cooled between 200 and 230 K, and which is generally attributed to interactions between hydrating solvent molecules and protein side chains. However, there is also experimental and theoretical evidence for a low-temperature transition in the intrinsic dynamics of the protein itself, absent any solvent. In the study by Bajaj et al., low-temperature solid-state NMR was used to examine site-specific fluctuations in atomic structure and dynamics in the absence of solvents. In particular, they employed MAS NMR to examine a structural phase transition associated with dynamic processes in a solvent-free polypeptide lattice at temperatures as low as 90 K. Several quantitative solid-state NMR experiments were employed to provide site-specific measurements of structural and motional features of the observed transition. 

Indirect determination of the enthalpy of unfolding assumes the knowledge of the equilibrium as a function of temperature. Starting from spectroscopic data spectroscopic signal for 100% denaturated (random coil) sample and 100% native protein was determined. The temperature range where protein transitions from native to denatured form was covered. Fraction of native protein as a function of temperature and the fraction of unfolded protein as a function of temperature /n and fo respectively, were defined in terms of measured absorbance A(T) as ... 

Thermodynamic parameters can be defined only for a reversible process. The midpoint corresponding to a thermally reversible folding-unfolding transition of a protein is defined by the temperature of transition, (i.e., the temperature at which the apparent transition constant K is equal to 1, and AG, the variation of free energy, is nul under conditions where a two-state approximation is valuable). Under these conditions is equal to AH/AS and AG is equal to AH(1 — T/T ). The different parameters are defined in Chapter 6 however, it is noted here that Privalov and Khechinaschvili (1974) have shown that AH is a linear function of temperature for a number... 

The key question we want to answer is what are the intrinsic sequence dependent factors tliat not only detennine tire folding rates but also tire stability of tire native state It turns out tliat many of tire global aspects of tire folding kinetics of proteins can be understood in tenns of tire equilibrium transition temperatures. In particular, we will show tliat tire key factor tliat governs tire foldability of sequences is tire single parameter... 

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