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How does carboxypeptidase demonstrate induced fit?

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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.

In the context of biochemistry, the induced-fit theory proposes that an enzyme is not a rigid structure but rather a flexible one that changes shape upon binding to a substrate. This conformational change is essential for aligning the enzyme's catalytic groups to facilitate a reaction.12

Carboxypeptidase serves as a primary example of this mechanism. When a substrate binds to the active site of carboxypeptidase, it induces a significant structural shift: a tyrosine molecule located at the active site moves by as much as 15 angstroms. This movement ensures that the catalytic groups are correctly positioned to interact with the substrate and form the necessary products. If a molecule is the wrong size, it fails to induce this specific alignment, preventing the reaction from occurring.12