Human Biochemistry, Volume 1 - Murray R. 1993

Structure and Functions of Proteins and Enzymes
Proteins: Structure and Properties
Denaturation

The relatively weak Bonds Responsible for stabilizing the secondary, tertiary, and Quaternary Structure of a protein are easily disrupted, leading to a loss of its biological activity. This disruption of the native structure is known as denaturation. From a physical perspective, denaturation can be viewed as the disorganization of the polypeptide chain conformation without any alteration of the Primary Structure. For a protomer, this process can be visualized as shown in Fig. 5.8.

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Fig. 5.8. Schematic representation of protomer denaturation.

The denaturation of an oligomeric protein results in its dissociation into protomers, which may or may not be accompanied by A change in their conformation.

Most Proteins lose their biological activity in the presence of strong mineral acids or bases, upon heating, and upon Treatment with ionic detergents (amphiphilic compounds), chaotropic agents (urea, guanidine), heavy metals (Ag, Pb, Hg), or organic Solvents. Denatured proteins are generally less soluble in Water and frequently precipitate out of aqueous solution. This property is widely utilized in clinical laboratories. Blood or serum samples collected for the analysis of small molecules (such as glucose, uric acid, or Pharmaceuticals) are first treated with trichloroacetic, phosphotungstic, or phosphomolybdic acid to precipitate the proteins. The precipitate is removed by centrifugation, and the protein-free supernatant is then analyzed.

The sensitivity of most Enzymes to heat, acids, and proteases allows for preliminary testing to determine whether a reaction is enzymatic in nature. If a Cell extract exhibits catalytic activity and loses it following boiling, acidification of the medium with subsequent neutralization, or treatment with a protease, it can be inferred that the catalyst is an enzyme.

The denaturation process is frequently influenced by the presence of a substrate. This effect is attributed to the Conformational Changes in the enzyme that accompany substrate binding. The resulting new conformation may be either more stable or less stable than the original one.