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How can changes in temperature or pH cause enzyme denaturation?

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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.

Enzymes are specialized protein molecules whose function depends on a precise three-dimensional structure, which is determined by their specific amino acid sequence. This structure creates an active site where substrates bind to catalyze reactions. Denaturation occurs when this structural integrity is lost, rendering the enzyme unable to function.12

Mechanisms of Denaturation

Temperature: Enzymes function optimally within specific physiological temperature ranges. High temperatures increase the kinetic energy of the molecule, which can disrupt the weak noncovalent bonds—such as hydrogen bonds and hydrophobic interactions—that maintain the enzyme's folded shape. Excessive cold can also alter an enzyme's shape, leading to a loss of activity.32
pH Changes: Enzymes have an optimum pH at which they are most efficient. Because the structure of a protein is sensitive to the acidity or basicity of its environment, significant shifts in pH can disrupt the chemical bonds holding the protein together. This deformation of the enzyme's structure, particularly at the active site, prevents it from binding to its substrate, thereby eliminating its catalytic ability.321

While some denaturation is reversible, it is often permanent, resulting in a total loss of biological activity.12