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Why can high temperatures permanently damage many enzymes?

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A multi-panel diagram illustrates how a substrate binds to an enzyme's active site through induced fit, leading to product formation, and shows how non-substrates and allosteric regulators can alter enzyme activity by binding to different sites on the enzyme. — Enzyme In the induced-fit theory of enzyme-substrate binding, a substrate approaches the surface of an enzyme (step 1 in box A, B, C) and causes a change in the enzyme shape that results in the correct alignment of the catalytic groups (triangles A and B; circles C and D represent substrate-binding groups on the enzyme that are essential for catalytic activity). The catalytic groups react with the substrate to form products (step 2). The products then separate from the enzyme, freeing it to repeat the sequence (step 3). Boxes D and E represent examples of molecules that are too large or too small for proper catalytic alignment. Boxes F and G demonstrate binding of an inhibitor molecule (I and I′) to an allosteric site, thereby preventing interaction of the enzyme with the substrate. Box H illustrates binding of an allosteric activator (X), a nonsubstrate molecule capable of reacting with the enzyme.

High temperatures can permanently damage enzymes through a process called denaturation.12

Enzymes are protein molecules whose biological activity depends on a specific three-dimensional shape, which is maintained by weak noncovalent bonds, such as hydrogen bonds and hydrophobic interactions. These bonds determine the folding pattern of the enzyme's amino acid chains, creating a precise active site where substrate binding occurs.1345

When an enzyme is exposed to high temperatures, the increased thermal energy disrupts these weak linkages. This causes the protein to lose its structural integrity, resulting in a looser, more random configuration. Because the enzyme's catalytic ability is strictly tied to its unique shape, this deformation prevents the enzyme from binding to its substrate, leading to a loss of biological activity. While some proteins can renature, the denaturation of many enzymes is irreversible, rendering them permanently nonfunctional.132