Proteins, hydration/volume

The voluminosity or hydration of interfacially bound protein may be calculated from the amount of water bound per gram of fat divided by the amount of protein bound per gram of fat. This corresponds to the volume of water per gram interfacial protein. Calculations show that emulsifiers facilitate interfacial protein hydration. This property is probably connected with their ability to desorb protein from the interface (Figure 14). 

Disaccharides can have similar utility to monosaccharides in DNA delivery polymers. Trehalose, a disaccharide composed of two glucose units linked via an a-(l—>1) glycosidic bond, has been shown to have cryo- and lyo-protective properties, attributed to an unusually large hydration volume [152]. As a function of these properties, trehalose has been shown to prevent aggregation and fusion of proteins and lipids [153]. Logically, incorporation of these features into a polymer backbone could afford similar characteristics to a DNA delivery system and may prevent aggregation of polyplexes in physiological serum concentrations and ionic... 

We can reasonably assume two major contributions to the difference in specific volume between the unfolded and folded states of a protein. The first contribution is that arising from the decrease in solvent-excluded volume when the tightly, but of course not perfectly, packed protein folded structure is disrupted. Water molecules enter this volume, thereby decreasing the overall volume of the protein solvent system. The magnitude of this contribution is a specific property of the protein, both in its folded and unfolded state. The second contribution arises from the change in the volume of the water molecules that hydrate the newly exposed protein surface area, relative to their volume in the bulk. Much of our present understanding of the contribution of differential hydration volume has come from recent studies of model compounds and proteins based on PPC. This technique, developed by Brandts and coworkers [17] and recently reviewed by us [16,18], is based on the measurement of the heat released or absorbed upon small (e.g., 0.5 MPa) pressure... 

Succinylation substantially increases specific volume of soy and leaf proteins (12,37). The succinylated soy protein becomes very fluffy and the color becomes much lighter, changing from a tan to a chalk white as the extent of derivatization is increased (12,47). No odors nor flavors were imparted by the succinylation process. Succinylation improved the whiteness and dispersibility characteristics of soy protein making it suitable for incorporation into coffee whiteners (47). Succinylated soy proteins hydrate rapidly on the tongue,""taste clean, but slightly acidic. It is not known if derivatization facilitates the removal of off-flavors from modified proteins. 

The attention of the reader is drawn to several books and reviews on protein hydration, in addition to the reviews by Kuntz and Kauzmann (1974) and by Edsall and McKenzie (1983). Recent volumes of Methods in Enzymology (Hirs and Timasheff, 1985 Packer, 1986) describe measurements on the hydration of protein and membrane systems. Saenger (1987) has reviewed aspects of macromolecule hydration. Edsall (1980) has given a brief history of research on water. Several summaries of current research in biophysics describe work related to the hydration of macromolecules (dementi and Chin, 1986 Ehrenberg et al., 1987 Moras et al., 1987 Welch, 1986). For comprehensive treatments of the properties of water and aqueous solutions, see the multivolume treatise by Franks (e.g., Franks, 1979), the review by Edsall and McKenzie (1978), and the volume by Eisenberg and Kauzmann (1969). 

The mass rado h is commonly used in describing protein hydration. Hydration, however, should depend more closely on protein surface than on volume or mass. Most of the data described in this review are for small globular proteins, for which weight and surface-based measures should be similar. Comparisons of proteins of much different size may need to take into account surface area, compactness, and domain size. 

A number of refinements and applications are in the literature. Corrections may be made for discreteness of charge [36] or the excluded volume of the hydrated ions [19, 37]. The effects of surface roughness on the electrical double layer have been treated by several groups [38-41] by means of perturbative expansions and numerical analysis. Several geometries have been treated, including two eccentric spheres such as found in encapsulated proteins or drugs [42], and biconcave disks with elastic membranes to model red blood cells [43]. The double-layer repulsion between two spheres has been a topic of much attention due to its importance in colloidal stability. A new numeri-... 

At ordinary pressure all the ionizable groups have their specific pK values and are present in ionized states according to these values. When pressure increases, we can expect all pK values to change, whereby the overall ionized state of the protein is changed. The whole hydration sheet may also be changed around the protein and conformational rearrangements may occur. This fact indicates that the volume of a protein may be very pressure-dependent. 

Ultracentrifugally sedimented micelles have a hydration of 1.6-2.7g H2Og 1 protein but voluminosities of 3-7mlg-1 have been found by viscosity measurements and calculation of specific hydrodynamic volumes. These values suggest that the micelle has a porous structure in which the protein occupies about 25% of the total volume. 

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