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How does substrate binding change an enzyme’s shape in induced-fit theory?

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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 induced-fit theory, the binding of a substrate to an enzyme does not merely involve a preformed active site. Instead, the substrate induces a conformational change in the enzyme’s shape, which is essential for the proper alignment of catalytic groups on the enzyme's surface.12

This process is often compared to a hand fitting into a glove, where the hand (substrate) causes the glove (enzyme) to adjust its shape. By shifting the enzyme's structure, the substrate ensures that the catalytic groups are positioned correctly to facilitate the reaction and form products. For instance, in the enzyme carboxypeptidase, substrate binding can cause a tyrosine molecule at the active site to move by as much as 15 angstroms.12

This flexibility allows enzymes to regulate activity; if a molecule is too bulky or small, it may cause a misalignment of these groups, preventing the reaction from occurring.12