Protein structures, compact stabilization mechanism

It is not always possible to apply enzymatic hydrolysis directly to proteins as they are in the native form. Native, globular proteins (e.g., from soy, corn, almond) or fibrous insoluble proteins (e.g., collagen, keratins, elastin) are generally resistant to proteolysis this is generally explained by the compact tertiary structure of the protein that protects most of the peptide bonds. In the denatured, unfolded form the peptide bonds are exposed and available for enzymatic cleavage. As native proteins in aqueous solution are in dynamic equilibrium with a number of more or less distorted forms, part of which can be considered denatured and thereby accessible to enzyme attack, the initial break of a few peptide bonds can destabilize the protein molecule and cause irreversible unfolding in some cases (e.g., hydrolysis of egg albumin by pepsin) this mechanism allows the protease to perform the hydrolysis to a remarkable extent. More frequently, especially when covalent bonds (disulfide bonds) stabilize the native form of the protein, a preliminary partial or extended denaturation is needed to make enzymatic hydrolysis possible this is normally achieved by heating or chemical attack, or a combination of the two. 

Proteins act in a similar way to polymeric stabilizers (steric stabilization). However, molecules with compact structures may precipitate to form small particles that accumulate at the oil/water interface. These particles stabilize the emulsions (sometimes referred to as Pickering emulsions) by a different mechanism. As a result of the partial wetting of the particles by the water and the oil, they remain at the interface. The equUibrium location at the interface provides the stability, since their displacement into the dispersed phase (during coalescence) results in an increase in the wetting energy. 

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