Protein properties

The properties of proteins depend on the amino acids that form them, whose protruding free radicals react with other molecules.

The active center of the protein is formed by the amino acids of a protein whose radicals have the ability to bind to and react with other molecules.

• Protein solubility.
• Denaturation and renaturation of proteins.
• Protein specificity.
• Protein buffer capacity.

In general, fibrous proteins are insoluble in water, while globular proteins are water soluble.

The globular proteins have a high molecular mass, so, to the dissolved, result in colloidal dispersions. In them, many of the apolar amino acids are located inside the protein, and in the polar ones, the free radicals (-R) of the polar amino acids are linked by hydrogen bonds with the water molecules that remain on the outside. In this way, the protein is covered by a layer of water molecules (solvation layer) that prevents it from binding to other proteins.

If this solvation layer disappears, there are interactions between different parts of the protein that will make it insoluble and will precipitate.

The denaturation of a protein occurs when the bonds holding the spatial configuration of the protein are broken, missing the secondary structures, tertiary (mainly) and quaternary. As a consequence of this, it loses its properties and cannot perform its function.

If unfavorable environmental changes occur in a colloidal protein dispersion, such as increased temperature, pH variations, alterations in the saline concentration of the medium, molecular agitation, etc., the bonds (hydrogen bonds, van der Waals forces, hydrophobic interactions, etc.) that maintain the globular conformation can be disrupted and the protein adopts the filamentous conformation. The protein will precipitate, but also, when the active center is altered, its properties will disappear and they will cease to be functional.

The denaturation does not affect the peptide bonds, but are affected disulfide bonds, the hydrogen bonds and weak interactions.

Sometimes, renaturation occurs, when upon returning to normal conditions, the protein regains its original conformation.

The denaturation can be:

• Irreversible. If the denatured protein cannot regain its native conformation and functionality.
• Reversibly. Renaturation occurs, recovering the protein its native conformation and functionality.

Some examples of denaturation in everyday life are when the milk is cut due to the denaturation of casein, the precipitation of egg white when the ovalbumin is denatured by the effect of heat, the "permanent" or fixing of a hairstyle of the hair by effect of the heat on the keratin of the hair, and so on.

De Alejandro Porto - Derivada de File:Protein folding.png de Emw, CC BY-SA 3.0, Enlace

Proteins, like the amino acids that compose them, have an amphoteric behavior. They tend to buffer the pH variations of the medium, since they can behave like an acid (releasing protons) or a base (capturing protons).