Enzyme Inhibitor – Enzymes and Enzyme Kinetics | Lecturio

Summary

This lecture delves into the mechanisms of enzyme inhibition, exploring both reversible and irreversible types. It covers competitive inhibition, where an inhibitor competes with the substrate for the enzyme's active site; non-competitive inhibition, where the inhibitor binds elsewhere, affecting enzyme function; and uncompetitive inhibition, which only targets the enzyme-substrate complex. Additionally, the lecture introduces suicide inhibition, an irreversible process where the inhibitor forms a covalent bond, permanently inactivating the enzyme. Understanding these mechanisms is essential for drug design and medical applications like antibiotic and cancer therapies.

Takeaways

• 😀 Enzyme inhibition plays a crucial role in both understanding enzymatic mechanisms and in medical applications, such as controlling bacterial infections or cancer cell growth.
• 😀 Competitive inhibition occurs when an inhibitor mimics the substrate and binds to the enzyme's active site, preventing the enzyme from properly interacting with the substrate.
• 😀 In competitive inhibition, increasing the substrate concentration can overcome the inhibitor's effect, eventually resulting in the same Vmax as the uninhibited enzyme.
• 😀 The apparent Km increases in competitive inhibition, indicating a reduced affinity of the enzyme for the substrate, although the actual affinity remains unchanged.
• 😀 In the Lineweaver-Burk plot for competitive inhibition, the Vmax remains the same, but the Km appears to increase due to the competitive interaction between the substrate and the inhibitor.
• 😀 Non-competitive inhibition differs from competitive inhibition because the inhibitor binds to a site other than the active site, and does not compete with the substrate.
• 😀 In non-competitive inhibition, the Vmax decreases because the inhibitor reduces the effective enzyme concentration, but the Km remains unchanged because the affinity of the enzyme for the substrate is not altered.
• 😀 In the Lineweaver-Burk plot for non-competitive inhibition, the lines cross at the same point on the x-axis (Km) but the y-intercept is higher, reflecting the reduction in Vmax.
• 😀 Uncompetitive inhibition occurs when the inhibitor binds only to the enzyme-substrate complex (ES complex), and this binding reduces both the apparent Vmax and Km.
• 😀 Suicide inhibition is an irreversible type of enzyme inhibition where the inhibitor forms a covalent bond with the enzyme, rendering the enzyme inactive permanently. Penicillin serves as an example of suicide inhibition, preventing bacteria from forming cell walls.

Q & A

What is the importance of enzyme inhibition in medical applications?

Enzyme inhibition is important because it allows us to control cellular processes. By inhibiting specific enzymes, we can stop harmful processes, such as bacterial infections or cancer cell proliferation, making it crucial for drug design and therapeutic strategies.

What is competitive inhibition, and how does it affect enzyme activity?

Competitive inhibition occurs when an inhibitor resembles the substrate and competes for the same active site on the enzyme. It lowers the enzyme's affinity for the substrate, which increases the apparent Km, but does not affect the V-max. The inhibition can be overcome by increasing the substrate concentration.

How does the presence of a competitive inhibitor affect the V-max and Km in an enzyme reaction?

The presence of a competitive inhibitor does not affect the V-max, as the inhibition can be overcome with enough substrate. However, the Km increases, indicating a reduced apparent affinity of the enzyme for its substrate.

What role does methotrexate play as a competitive inhibitor?

Methotrexate is similar to dihydrofolate, the natural substrate for dihydrofolate reductase. By binding to the enzyme's active site, methotrexate inhibits the enzyme, preventing nucleotide production, which is crucial for cell division. This is why methotrexate is used as a chemotherapy agent.

How does non-competitive inhibition differ from competitive inhibition?

Non-competitive inhibition occurs when the inhibitor binds to a different site on the enzyme, not the active site. This inhibits the enzyme regardless of the substrate concentration, leading to a decrease in V-max but no change in Km.

What happens to the V-max and Km when a non-competitive inhibitor is present?

In the presence of a non-competitive inhibitor, the V-max decreases because the enzyme is less effective. However, the Km remains unchanged since the enzyme's affinity for the substrate is unaffected by the inhibitor.

Why does a non-competitive inhibitor not compete with the substrate for the active site?

A non-competitive inhibitor binds to a site other than the enzyme's active site, which means it does not directly compete with the substrate for binding to the active site. This leads to a fixed reduction in the enzyme's activity, independent of substrate concentration.

What is uncompetitive inhibition, and how does it impact enzyme function?

Uncompetitive inhibition occurs when the inhibitor binds only to the enzyme-substrate complex. This reduces both the V-max and Km, making it appear that the enzyme has a higher affinity for the substrate, as the inhibitor stabilizes the enzyme-substrate complex.

How does uncompetitive inhibition affect the Lineweaver-Burk plot?

On a Lineweaver-Burk plot, uncompetitive inhibition is represented by a line with a higher intercept on the y-axis (indicating a lower V-max) and a shifted x-axis intercept (indicating a lower Km). This reflects the changes in both the apparent affinity and maximum reaction velocity.

What is suicide inhibition, and how does it differ from other types of inhibition?

Suicide inhibition is an irreversible form of enzyme inhibition where the inhibitor binds covalently to the enzyme, permanently deactivating it. Unlike competitive, non-competitive, and uncompetitive inhibition, which are reversible, suicide inhibition results in permanent enzyme inactivation. An example is penicillin, which irreversibly inhibits bacterial enzymes involved in cell wall synthesis.