Lysozyme melting temperatures

Lysozyme Melting temperature Cation effect (Cl as common anion) ... 

Lysozyme from bacteriophage T4 is a 164 amino acid polypeptide chain that folds into two domains (Figure 17.3) There are no disulfide bridges the two cysteine residues in the amino acid sequence, Cys 54 and Cys 97, are far apart in the folded structure. The stability of both the wild-type and mutant proteins is expressed as the melting temperature, Tm, which is the temperature at which 50% of the enzyme is inactivated during reversible beat denat-uration. For the wild-type T4 lysozyme the Tm is 41.9 °C. 

Figure 17.4 Melting temperatures, Tm, of engineered single-, double-, and tripledisulfide-containing mutants of T4 lysozyme relative to wild-type lysozyme. The red bars show the differences in Tm values of the oxidized and reduced forms of the mutant lysozymes. The green bars for the multiple-bridged proteins correspond to the sum of the differences in Tm values for the constituent single-bridged lysozymes. (Adapted from M. Matsumura et al.. Nature 342 291-293, 1989.)...

Fig. 2. Electrophoretic demonstration of amplified lysozyme cDNA. The primers used were oligo(dT) and a lysozyme-specific primer. The templates were mRNAs purified from stomach mucosa of (1) cow, (2) sheep, and (3, 4) axis deer lane, 5 contained no mRNA. Separations were performed in a 1% agarose gel of low melting temperature. The lysozyme cDNA product is approximately 900 bp in all species. In lane 4 the axis deer product was digested with Pstl, which cuts at an internal site, giving a visible product of 700 bp. The molecular weight markers (0X174 DNA digested with Hindi) were run in lane M.

As an example, we will consider the molecular dynamical behavior of egg white lysozyme. The temperature dependence of mobility of fluorescence, spin and Mossbauer labels attached to lysozyme was found to be similar to other investigated proteins the monotonic increase typical for rigid polymers in dry states and in samples with water content (wt) was less than the critical value (wtcr) and drastically burst when wt > wtcr at T > 200 K took place (Frolov et al., 1978 Likhtenshtein, 1979). At similar conditions, experiments on the temperature dependence of heat capacity indicated only a monotonic steady increase for rigid organic material. Recently, in the fully dried lysozyme crystal, similar monotonic behavior of heat capacity was observed in temperatures between 8 and 30°C. At D20 content more than 24 wt %, a slight deviation from the monotony was observed at temperatures above approximately 185 K, which most probably is due to the eutectic melting of NaCl/2H20 present in the samples to prevent water crystallization (Miyazaki et al., 2000). 

Scanning calorimetric measurements of the denaturatlon process as a function of extent of hydration have been reported for several proteins (8-lactoglobulin (12) lysozyme (13)). The melting temperature rises and other parameters of the denatura-tion transition change as the hydration level is decreased below... 

At 298 K, the enthalpy of denatiu on of hen egg white lysozyme is +217.6 kJ mol and the change in tbe constant-pressure molar heat capacity resulting from denaturation of tbe protein is +6.3 kJ K mol", (a) Estimate the enthalpy of denaturation of the protein at (i) 351 K, the melting temperature of the macromolecule, and (ii) 263 K. State any assumptions in your calculations, (b) Based on your answers to part (a), is denaturation of hen egg white lysozyme alsrays endotbermic ... 

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