Lysozyme specific heat capacity

Fig. 2. Temperature dependence of the partial specific heat capacity for pancreatic ribonuclease A (RNase), hen egg-white lysozyme (Lys), sperm whale myoglobin (Mb), and catalase from Thermus thermophilus (CTT). The flattened curves are for RNase and Lys with disrupted disulfide cross-links and for apomyoglobin, when polypeptide chains have a random coil conformation without noticeable residual structure (Privalov et al., 1988).

Figure 4 gives the apparent specific heat capacity [< >(Cpj)] of lysozyme... 

Fig. 4. The apparent specific heat capacity of lysozyme from 0 to 0.45 g of water per gram of protein. The curve is calculated. The heat capacity measurements were made with lyophilized powders of lysozyme, appropriately hydrated, except for the four measurements indicated by the square symbols, for which the sample was a film formed by slowly drying a concentrated solution of lysozyme. From Yang and Rupley (1979).

Fig. 38. Comparison of heat capacity and spectroscopic properties. Effect of hydration on lysozyme time-average properties. (Curve a) Carboxylate absorbance (1580 cm" ) (curve b) amide I shift ( 1660 cm" ) (curve c) OD stretching frequency (—2570 cm ) (curve d) apparent specific heat capacity (curve e) diamagnetic susceptibility. From Rupley elal. (1983).

Figure 2. Apparent specific heat capacity of lysozyme from 0 to 0.45 g of water...

Figure 4.37 Temperature dependence of partial specific heat capacity of lysozyme in solution at pH 4.5. Sample concentration, 1.8 g 1 heating rate, 1 "C min sensitivity on heating, 4.18x10 "J C ...

Fig. 3. Specific heat of the lysozyme-water system from 0 to 1.0 weight fraction of protein. Least-squares analysis of the linear portion of the heat capacity function from 0 to 0.73 weight fraction of water gives = 1.483 0.009 J K g ...

The process of protein hydration is the stepwise addition of water to dry protein, until the hydration end point is reached. Heat capacity measurements (Yang and Rupley, 1979) serve as a framework on which to develop a picture. Figure 38 gives the dependence on hydration level of various time-average properties of lysozyme, over the hydration range 0-0.4 h, from the dry protein to slightly beyond the end point of the process. Curve d shows the dependence of the apparent specific heat on hydration level. It is directly related to the extent to which the thermal response of the lysozyme-water system deviates from ideal behavior. The nonideality of the system shows three discontinuities at 0.07, 0.25, and 0.38 h. 

Since the values of the thermal diffusivity for myoglobin and water are close, the discrepancy between their thermal conductivities is largely due to differences in their respective heat capacities. At 300 K the specific heat of water is 4.2 J K 1 g-1, whereas we calculate the specific heat of myoglobin to be 1.0 J K 1 g 1 at 300 K. This latter value is reasonably close to measured specific heats for proteins. For example, the specific heat of lysozyme in dilute aqueous solution is 1.5 J K-1 g , and it is 1.3 J K-1 g-1 for the dry protein [154,155]. Still, we should bear in mind that at 300 K the partial specific heat of a hydrated protein may be some 50% larger than the specific heat of a dry protein [156], so that the coefficient of thermal conductivity may be correspondingly larger. 

---