All proteins in a living system possess definite configuration and biological activity. A protein found in a living system with definite configuration and biological activity is called a native protein. When a protein in its native form is subjected to physical change such as change in
temperature, addition of solvents miscible with water or chemical change such as addition of acids, alkalies or salts, the hydrogen bonds are disturbed. As a result, globules unfold
and helix get uncoiled and protein loses its biological activity and gets coagulated. The proteins in this state are said to be denatured.
The process that brings about changes in physical as well, as biological properties of the proteins is called denaturation of proteins.
Some important features of denaturation are
i. Chemically, denaturation does not change the primary structure but changes the secondary and tertiary structures of proteins.
ii. Denaturation of proteins can be caused by changes in pH, temperature or by adding other denaturating agents.
iii. Denatured protein loses its biological activity.
iv. During denaturation, the protein molecule uncoils from an ordered and specific conformation into a more random conformation leading to precipitation. Thus, denaturation leads to increase in entropy.
v. Denaturation may be reversible or irreversible.
The most common example of irreversible denaturation of proteins is coagulation of albumin present in white part of an egg. When the egg is boiled, hard the soluble globular proteins present in it denature resulting in the formation of insoluble fibrous proteins.
Another example of irreversible denaturation is curdling of milk which is caused due to formation of lactic acid by bacteria present in milk.
In case of reversible denaturation process, the proteins recovers its original properties and biological activity when the disruptive agent is removed. The reverse of denaturation is called renaturation.