🧭 Types of Enzyme Inhibitors

There are two main types:

1. Competitive Inhibitors

Think of musical chairs: Two people (the substrate and the inhibitor) are competing to sit on the same chair (active site).

• A competitive inhibitor looks very similar to the normal substrate.
• It goes to the same active site where the substrate normally fits.
• If the inhibitor gets there first, it blocks the enzyme so that the real substrate cannot attach.

🔹 Example: Malonic Acid vs. Succinic Acid

• The enzyme succinic dehydrogenase helps change succinic acid into fumaric acid.
• Malonic acid looks very similar to succinic acid.
• So malonic acid competes with succinic acid to attach to the enzyme.
• If malonic acid wins, the enzyme is blocked temporarily.

2. Non-Competitive Inhibitors

Think of a remote control: Instead of sitting in the chair (active site), the inhibitor presses a button on the side (a different spot), and the chair changes shape so no one can sit on it.

• These inhibitors do not look like the substrate.
• They attach to the enzyme at a different spot, not the active site.
• But when they attach, they change the enzyme’s shape.
• Because of this change, the active site no longer fits the substrate, and the enzyme can’t work.

🔹 Example: Succinyl-CoA

• The enzyme succinyl-CoA synthetase makes a product called succinyl-CoA.
• After being made, succinyl-CoA comes back and attaches to the enzyme (not on the active site).
• It changes the enzyme’s shape, stopping it from working further.
• This is like a feedback system to prevent making too much product.

🔄 Reversible vs. Irreversible Inhibitors

Reversible Inhibitors

Think of a magnet stuck to your fridge—you can easily remove it.

• They bind weakly to the enzyme (using hydrogen bonds).
• You can remove them by:
  • Diluting the solution
  • Washing it
  • Increasing the amount of substrate
• Once removed, the enzyme works again.

🔹 Example: Malonate

• Temporarily blocks the enzyme succinate dehydrogenase.
• If removed, the enzyme works again. So, the effect is temporary.

Irreversible Inhibitors

Think of super glue on a machine part—it’s stuck permanently and can’t be undone.

• These inhibitors form strong covalent bonds with the enzyme.
• The enzyme is permanently damaged and cannot be reused.
• Even if you add more substrate, the enzyme stays inactive.

🔹 Example: Penicillin

• Penicillin blocks the enzyme bacteria need to build cell walls.
• Once blocked, the bacteria cannot survive, which is why penicillin is a powerful antibiotic.