How do competitive inhibitors affect enzyme activity?

Competitive inhibitors reduce enzyme activity by blocking the active site, preventing substrate binding.

Competitive inhibitors are molecules that have a similar structure to the substrate of an enzyme. They compete with the substrate for the active site of the enzyme, hence the term 'competitive'. When a competitive inhibitor binds to the active site, it prevents the substrate from binding, thereby reducing the enzyme's activity. This is because the enzyme-substrate complex, which is necessary for the reaction to occur, cannot be formed.

The effect of competitive inhibitors on enzyme activity can be overcome by increasing the concentration of the substrate. This is because as the substrate concentration increases, the likelihood of a substrate molecule colliding with the enzyme and binding to the active site, rather than the inhibitor, also increases. Therefore, the presence of a competitive inhibitor increases the apparent Km (Michaelis constant) of the enzyme, which is the substrate concentration at which the reaction rate is half its maximum. However, the Vmax (maximum reaction rate) remains the same, as it can still be reached if the substrate concentration is high enough.

It's important to note that competitive inhibitors are not permanently bound to the enzyme. They bind and unbind from the active site, allowing for the possibility of the substrate to bind. This is different from non-competitive inhibitors, which bind to an allosteric site (a site other than the active site) on the enzyme and cause a conformational change in the enzyme structure, preventing substrate binding regardless of the substrate concentration.

In summary, competitive inhibitors reduce enzyme activity by competing with the substrate for the active site on the enzyme. This prevents the formation of the enzyme-substrate complex and thus the reaction from occurring. However, the effect of competitive inhibitors can be overcome by increasing the substrate concentration, as this increases the chance of the substrate, rather than the inhibitor, binding to the enzyme.