0.2 0.3 1/P (atm)

Figure 1 .11 (A) Plots of h(g-water/g-protein) versus the inverse of osmotic pressure1/P gives linear plots for which the slope varies as the inverse of the effective molecular weight and the constant is the solute solvent interaction parameter expressing hydration encapsulated by the protein henc (Fullerton et a/., 1993). The value henc includes water bridges, dielectric water clusters, and bulk water fraction that are encapsulated inside the protein such that they are excluded from thermodynamic solution expressions for osmotic pressure and freezing depression. Encapsulated water molecules never interact with the osmotic membrane but can change dramatically, as shown in Figure 1.12 with solution parameters and most especially with pH. Under native condition, however, the measured henc —> hM(nat) as it does here for hemoglobin. (B) Reevaluation of RBC volume measurements as a function of osmotic pressure show that the henc = hM(nat) = 1.7 g/g in the isotonic region. There are changes in the henc in the hypotonic and hypertonic regions. Reproduced with permission from Fullerton et a/. (2006a .

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