Sorption lysozyme

Fig. 13. Relative sorption capacity of proteins by carboxylic CP Biocarb-T vs pH of solution 1) terrilytin, 2) insulin, 3) chymotrypsinogen, 4) pancreatic ribonuclease, 3) pepsin, 6) thymarine, 7) thermolysine, 8) haemoglobin, P) lysozyme. mma, — quantity of protein bonden on Biocarb-T by pHma (...

A typical isotherm, for lysozyme, is shown in Fig. 1. There is a knee at 0.05—0.1 h (g of water per g of protein, mass ratio) and a strong upswing to the isotherm near 0.25 h. Sorption measurements on model polymers and chemically modified proteins (see Watt and D Arcy, 1976 ... 

Fig. 1. DjO sorption isotherm for lysozyme at 27°C. The data were fit by a model with three classes of sorption sites, to give curves (a), (b), and (c). From Careri el al. (1979b).

Lioutas et al. (1986) measured the 0 and resonances of lysozyme powders and solutions, in experiments like those carried out for H by Fullerton et al. (1986). They similarly interpreted discontinuities in the NMR response in terms of three populations of water 20 mol of water per mol of protein (corresponding to 0.025 h) with a correlation time of 41 psec, 140 mol of water (0.17 h) with a correlation time 27 psec, and 1400 mol of water (1.7 h) with a correlation time 17 psec. The differences between these results and those of Fullerton et al. (1986) indicate the difficulty of estimating water correlation times. Lioutas et al. (1987) extended these results by analyzing H resonance data through comparison with the sorption isotherm. D Arcy-Watt analysis of the sorption isotherm gave 19 mol of tightly bound water per mol of lysozyme, 148 mol of weakly bound water, and 2000 mol of multilayer water. These classes plus two more types, corresponding to water in solutions... 

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. 

Calculated by integration of the sorption isotherm measured for lysozyme at 27°C (Hno-jewyj and Reyerson, 1959). 

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. 

The dependence of the heat of sorption on the extent of coverage has been observed to be Irregular, with an extremum in the knee region of the isotherm (, 7). A calorimetric study W has demonstrated a similar Irregularity in the hydration of polysaccharides. The extremum in the heat of sorption for lysozyme ( ) corresponds with one in the heat capacity (see below) that reflects proton redistribution. 

As noted already, the hydration level above which the protein heat capacity is constant defines completion of the hydration process. The value estimated for lysozyme is 0.38 g of water/g of protein, equivalent to 300 molecules of water/molecule of lysozyme. With regard to other thermodynamic measurements, the sorption Isotherm is not able to define completion of the hydration process, and there can be difficulty in Interpreting scanning calorimetric experiments in terms of completion of hydration, because different states of the system are being compared (frozen and solution, or native and denatured) and during a scanning calorimetric measurement the system is not at equilibrium, allowing reaction rates to influence the response. 

By a combined gravimetric and i.r. technique, spectra of lysozyme protein films have been recorded during sorption isotherms at constant water content h (mg per mg dry protein) in the range 0Computer-aided differential analysis shows the effect of progressive hydration on some significant sites of the protein such as the ionizable acidic side-chains and the backbone amide carbonyls, as well as the spectrum of the absorbed water itself. In order to derive thermodynamic properties of these sites, the... 

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