Enzyme Inhibition: Videos & Practice Problems

Enzyme inhibitors are compounds that decrease an enzyme's initial reaction velocity (v₀). They achieve this by forming complexes with either the free enzyme (E) or the enzyme-substrate complex (ES), leading to the formation of EI or ESI complexes. By binding to these forms, inhibitors interfere with the enzyme's ability to catalyze reactions, effectively slowing down or halting the production of the reaction's products. This regulation is crucial for cellular processes and can also be used in medicine to treat diseases by targeting specific enzymes.

There are several types of enzyme inhibitors, each affecting enzyme activity in distinct ways. These include:

• Irreversible inhibitors: Also known as inactivators, they form a permanent bond with the enzyme.
• Reversible inhibitors: These can dissociate from the enzyme, allowing for temporary inhibition.
• Competitive inhibitors: They compete with the substrate for the active site of the enzyme.
• Uncompetitive inhibitors: They bind only to the enzyme-substrate complex, not the free enzyme.
• Mixed inhibitors: They can bind to both the free enzyme and the enzyme-substrate complex.
• Non-competitive inhibitors: They bind to an allosteric site, not the active site, affecting enzyme activity regardless of substrate presence.

Cells use enzyme inhibitors for two main purposes: regulation of enzyme activity and defense against pathogens. For regulation, cells produce inhibitors to control the rate of enzyme-catalyzed reactions, ensuring that product levels remain balanced. For defense, cells can secrete inhibitors to act as poisons against harmful bacteria or pathogens. These inhibitors can either bind to the free enzyme or the enzyme-substrate complex in the pathogen, inhibiting its metabolic processes and protecting the cell from infection.

In competitive inhibition, the inhibitor competes with the substrate for binding to the enzyme's active site. This type of inhibition can be overcome by increasing the concentration of the substrate. In contrast, non-competitive inhibition involves the inhibitor binding to an allosteric site, which is different from the active site. This binding changes the enzyme's conformation, reducing its activity regardless of the substrate concentration. Therefore, non-competitive inhibition cannot be overcome by simply increasing the substrate concentration.

Enzyme inhibitors are crucial in medicine because they can be used to treat various diseases by targeting specific enzymes involved in disease pathways. For example, certain inhibitors can block enzymes that contribute to cancer cell growth, viral replication, or bacterial infections. By inhibiting these enzymes, the drugs can slow down or stop the progression of the disease, providing an effective treatment option. Additionally, enzyme inhibitors are used in managing conditions like hypertension, diabetes, and neurodegenerative diseases.