in biology, process modifying the molecular structure of a protein. Denaturation involves the breaking of many of the weak linkages, or bonds (e.g., hydrogen bonds), within a protein molecule that are responsible for the highly ordered structure of the protein in its natural (native) state. Denatured proteins have a looser, more random structure; most are insoluble. Denaturation can be brought about in various ways—e.g., by heating, by treatment with alkali, acid, urea, or detergents, and by vigorous shaking.

The original structure of some proteins can be regenerated upon removal of the denaturing agent and restoration of conditions favouring the native state. Proteins subject to this process, called renaturation, include serum albumin from blood, hemoglobin (the oxygen-carrying pigment of red blood cells), and the enzyme ribonuclease. The denaturation of many proteins, such as egg white, is irreversible. A common consequence of denaturation is loss of biological activity (e.g., loss of the catalytic ability of an enzyme).