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Why can increasing substrate concentration reduce the effects of competitive inhibition?

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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 competitive inhibition, an inhibitor molecule and the substrate compete for the same binding site on an enzyme. Because the inhibitor binds to the enzyme reversibly, the two molecules are in a constant state of competition for the active site.12

Increasing the concentration of the substrate shifts this balance in favor of the substrate. By flooding the environment with more substrate molecules, the probability of a substrate molecule encountering and binding to an available active site increases significantly, while the relative likelihood of an inhibitor occupying that site decreases. Consequently, if the substrate concentration is high enough, it can effectively outcompete the inhibitor, allowing the enzyme to reach its maximal reaction velocity despite the presence of the inhibitory compound.234