Lysozyme enthalpy

TABLE 6.1. Gas-Phase Enthalpies that Can Be Used to Determine the Energies of the Different Configurations Involved in the Catalytic Reaction of Lysozyme ... 

Figure 16.9 The ratio of the effective calorimetric enthalpy to the enthalpy calculated by the van t Hoff method from optical measurements, plotted against the temperature of denaturation. The symbols represent the following proteins , metmyoglobin A, ribonuclease O, cytochrome c O, a-chymotrypsin , lysozyme. Reproduced by permission from P. L. Privalov, Adv. Prot. Chem., 33, 167 (1979).

Hen egg-white lysozyme, lyophilized from aqueous solutions of different pH from pH 2.5 to 10.0 and then dissolved in water and in anhydrous glycerol, exhibits a cooperative conformational transition in both solvents occurring between 10 and 100°C (Burova, 2000). The thermal transition in glycerol is reversible and equilibrium follows the classical two-state mechanism. The transition enthalpies AHm in glycerol are substantially lower than in water, while transition temperatures Tm are similar to values in water, but follow similar pH dependences. The transition heat capacity increment ACp in glycerol does not depend on the pH and is 1.25 0.31 kj (mol K) 1 compared to 6.72 0.23 kj (mol K)-1 in water. Thermodynamic analysis of the calorimetric data reveals that the stability of the folded conformation of lysozyme in glycerol is similar to that in water at 20-80°C but exceeds it at lower and higher temperatures. 

Figure 8. A DSC record (a thermogram) from a thermally induced transition of lysozyme in dilute aqueous solution. Tt = transition temperature ACp = change in heat capacity accompanying the unfolding process. The hatched area is proportional to the enthalpy of transition. Adapted from Privalov (1980).

The molecular mechanisms by which the extension of the N-terminus by the extra methionine residue destabilized recombinant a-lactalbumin remain unclear. Additional conformational entropy of the extra methionine residue in the unfolded state could account for the destabilization and unfolding-rate acceleration of the recombinant protein [22]. Ishikawa and coworkers reported the destabilization of recombinant bovine a-lactalbumin, similarly induced by the extra N-terminal methionine residue, and showed that the enthalpy change of thermal unfolding was the same for the authentic and recombinant proteins, indicating that the destabilization was caused by an entropic effect [42]. However, the destabilization by the extra methionine residue in the lysozyme homologous to a-lactalbumin was rather enthalpic and accompanied by a disruption of hydrogen-bond networks in the N-terminal region [43,44]. 

The diamagnetic susceptibility is a measure of the averaged electronic distribution in bulk matter. Careri et al. (1977, 1980) showed that the differential diamagnetic susceptibility per gram of water adsorbed on lysozyme powders reached the bulk water value at 0.2 h. Lysozyme behaved as a normal diamagnetic substance. The diamagnetic susceptibility and the enthalpy of sorption for lysozyme change similarly at low hydration. 

From the difference between the free energy and enthalpy of hydration. The two small globular proteins, lysozyme and ribonuclease, perhaps can be considered compatible at this level of comparison. 

Pfeil (1981) concluded that a-lactalbumin is less stable than lysozyme, with a lower thermal transition temperature, lower denaturational enthalpy, lower heat capacity change, and lower Gibbs free-energy change. 

Smith, A.L., Shirazi, H.M., and Mulligan, S.R. Water sorption isotherms and enthalpies of water sorption by lysozyme using the quartz crystal micro-balance/Heat-conduction calorimeter, Biochim. Biophys. Acta — Protein Struct. Mol. Enzymol., 1594,150, 2002. 

A hybrid QCM/calorimetry device, Masscal, has been developed recently [199]. This technique combines the mass measurement change upon gas adsorption with the accompanying isothermal heat flow that allows a molar binding enthalpy to be determined. Various thin film chemical and biochemical systems have been studied, such as the hydration isotherms and associated hydration enthalpies determined for the immobihzed enzyme lysozyme [200]. 

For HyHel5-lysozyme, the calculated enthalpy and free enthalpy changes are in good agreement with the experimental values at 25°C. 

FIGURE 13.14 Dependence of the denaturation enthalpy on the denaturation temperature for (a) lysozyme and (b) a-lactalbumin, both dissolved in 0.05 M phosphate buffer pH 7. (Adapted from Haynes, C.A. and Norde, W., J. Colloid Interface ScL, 169, 313, 1995.)... 

The simulation results for the MSD of both protein and DNA find that (A ) changes its functional form below Tp 245K for both lysozyme and DNA. Using numerical differentiation of the total enthalpy of the system (protein and water), Cp has been calculated, by fitting the simulation data for enthalpy with a fifth-order polynomial, and then taking the derivative with respect to T. Figure 12a shows the maxima of Cp T) at 7w 250 lOK for both biomolecules. 

The heat capacity of protein unfolding. Figure 30.1.3 shows the enthalpy of folding T4 lysozyme. 

Another phase change is the denaturation of a protein from a normal, folded state to a disrupted, unfolded state-just like what happens when an egg is cooked. The Clausius-Clapeyron equation is applicable, but here the "pressure" of the phase is equal to the fraction that is denatured at a particular temperature. Lysozyme, an enzyme that breaks down bacterial cell walls, has an enthalpy of denaturation, AdenW, that is 160.8 kJ/mol. If the denatured fraction of lysozyme, fdeiv is 0.113 at 45.0°C, what is fjen 75.0°C ... 

Avidin is a basic glycoprotein (Table 11.5). Its amino acid sequence has been determined. Noteworthy is the finding that 15 positions (12% of the total sequence. Table 11.7) are identical with those of lysozyme. Avidin is a tetramer consisting of four identical subunits, each of which binds one mole of biotin. The dissociation constant of the avidin-biotin complex at pH 5.0 is k i/ki = 1.3 x 10 mol/1, i. e., it is extremely low. The free energy and free enthalpy of complex formation are AG = — 85kJ/mole and AH = —90kJ/mole, respectively. Avidin, in its form in egg white, is practically free of biotin, and presumably fulfills an antibacterial role. Of interest is the occurrence of a related biotin-binding protein (streptavidin) in Streptomyces spp., which has antibiotic properties. 

The dependence on pH of the free energies and enthalpies of the interactions of mono- and di-saccharides with lysozyme has been measured. ... 

Figure 1.27 shows the experimental DSC scan of hen white lysozyme (G. Privalov et al.. Anal Biochem. 79,232 (1995)) converted to kilojoules (from calories). Determine the enthalpy of unfolding of this protein by integration of the curve and the change in heat capacity accompanying the transition. 

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 ... 

The protein lysozyme, sm enzyme that brejiks down bactericd cell walls, unfolds at a tTcuisition temperature of 75.5 C, md the stcmdcffd enthalpy of transition as determined using differential scanning calorimetry is +509 kj mol". It follows that... 

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