Fundamentals of Biochemistry - Filippovich, Y. B. 1999

Proteins
Properties of Proteins

The properties of Proteins are conventionally divided into chemical, physical, and biological.

The chemical properties of proteins are exceptionally diverse. Containing amino acid radicals of various chemical natures, protein macromolecules are capable of undergoing a wide range of reactions. These reactions, already listed in our Structure/133.html">Discussion of amino acid properties, are entirely characteristic of proteins as well.

Of particular importance in determining specific Structural Features of protein molecules and many of their biological properties are interactions between the side chains (radicals) of amino acid residues within the same protein molecule. These interactions reveal a clear dependence of protein tertiary structure on various environmental conditions, such as ambient pH, salt concentration in solution, the redox state of The Cell, and others. The types of these reactions are illustrated in Fig. 35. The Hydrolysis of peptide bonds is also highly characteristic of proteins. Possessing a significant number of basic and acidic groups, proteins exhibit amphoteric properties.

Certain physical properties of proteins—such as molecular weight, birefringence, and electrophoretic mobility—were discussed above. In addition, proteins exhibit optical properties, which include The ability to rotate the plane of polarized light (optical activity), scatter light due to the considerable size of protein particles, and absorb ultraviolet radiation. These optical properties are widely utilized in quantitative protein assays, molecular weight determination, and related Applications.

A key physical property of proteins is their ability to adsorb low-molecular-weight Organic compounds and ions on the molecular surface (and occasionally encapsulate them within the molecule). This property underlies the transport function of proteins in living organisms, as certain proteins serve as efficient carriers of metabolic products.

The biological properties of proteins primarily include their biocatalytic activity. Owing to their unique molecular architecture or the presence of an active group bound to the protein, many proteins can catalytically accelerate Chemical Reactions. This property plays a vital role in sustaining life processes and will be examined in detail in the chapter on Enzymes. Another equally important biological property is hormonal activity, which is the ability to regulate entire networks of reactions in the Organism. Furthermore, certain proteins exhibit toxic properties, pathogenic activity, protective and receptor functions, trigger behavior, and mediation of Cell Adhesion—thereby driving morphogenesis and related processes.

Proteins also play a tremendous structural role: combined with other macromolecules, they form complex Biopolymers such as Nucleoproteins, Lipoproteins, and Glycoproteins, which in turn give rise to subcellular structures and supramolecular assemblies within the organism. Notably, the precise information required to build a given subcellular structure is encoded directly within the protein molecules. The unique combination of chemical, physical, and biological properties secures for this Class of organic compounds a central role in all life phenomena.

Another unique characteristic of protein bodies is Denaturation. Proteins that retain all their native, characteristic properties are referred to as native proteins. Often, even under very mild treatments—such as gentle shaking—and certainly under harsh physical or chemical influences, proteins rapidly lose their Native State and undergo denaturation. The disruption of the unique structure of a native protein, accompanied by the loss of its characteristic properties (such as solubility, biological activity, and electrophoretic mobility), is termed denaturation. As a rule, denaturation affects the tertiary and partially Introduction/11.html">Secondary structure of the protein molecule without altering its Primary Structure. Consequently, denaturation primarily disrupts disulfide bridges, salt bridges, and Hydrogen Bonds, as well as hydrophobic interactions within the protein molecule. Under specific conditions, a denatured protein can be partially or fully restored to its original state, a process known as renaturation. Modern fundamental biology pays close attention to the disruption of native protein conformation, linking it to critical cellular functions and, specifically, to the denaturation-based mechanisms of cellular injury.