Water layer hypothesis, protein

Secondly, the water layer hypothesis proposes that the stabilization of proteins is achieved by the trapping of water molecules close to the biomolecular surface (Belton and Gill, 1994). The protein stabilization conferred by the excipients during dehydration is brought about primarily by these excipients substituting for water molecules on the surface of the protein. 

In another set of studies, it has been reported that the in vitro digestibility of lipid droplets by pancreatic lipase is significantly affected by emulsifier type (Mun et al, 2006, 2007 Park et al., 2007). Intuitively, one might expect that a thick dense layer of strongly bound protein-polysaccharide complex at the oil-water interface would reduce considerably the in vivo accessibility of lipases, and hence would reduce the rate of human metabolism of fats. Establishment of the validity of this hypothesis must still await consolidation of a substantial body of detailed results from independent systematic studies on a broad range of mixed biopolymer systems. 

Proteins are known to become extensively denatured or unfolded at the air/water interface (15). Similar but perhaps less extensive perturbation of a protein s structure by the aqueous/solid interface is therefore often a reasonable but unproven assumption. The idea that proteins unfold to different extents on different polymers, thus eliciting differences in cellular response by the polymers, is a major alternative hypothesis to the possible compositional variation in the adsorbed layer. Therefore, the structure of proteins at solid interfaces has been the subject of many studies. 

Ions can significantly influence the structure of water at interfaces. Hydration can be caused by the overlap of layers of hydrated ions adsorbed on the surfaces. On mica, for example, the dehydration of adsorbed cations is most likely the main cause for the short-range repulsion between two approaching surfaces [451]. Computer simulations between smooth hydrophilic surfaces confirm a layered structure of the water molecules and as a result a periodic force [1159,1160]. Paunov et al. [1171] used this hypothesis to explain the interaction between proteins in suspensions. 

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