Concept preview

What you will be able to do

1. 01Explain what an enzyme inhibitor is and distinguish competitive from non-competitive (allosteric) inhibitors.
2. 02Distinguish reversible from irreversible inhibition.
3. 03Explain the roles of cofactors, coenzymes and vitamins in enzyme function.
4. 04Describe feedback (end-product) inhibition and its role in controlling metabolic pathways.
5. 05Interpret how substrate concentration affects competitive versus non-competitive inhibition.

Speeding enzymes up is only half the story of controlling a cell; being able to slow them down or switch them off is just as important. A molecule that reduces or stops an enzyme's activity is called an inhibitor, and inhibitors are everywhere in biology and medicine. Your own cells use them to regulate their chemistry from moment to moment, switching pathways on and off as needs change. Many medicines are enzyme inhibitors — some antibiotics disable bacterial enzymes, aspirin blocks an enzyme involved in pain and inflammation, and many poisons kill precisely because they inhibit a vital enzyme. Understanding inhibition therefore links the abstract chemistry of the active site to pharmacology, toxicology and the everyday control of metabolism. Inhibitors fall into two great families depending on where on the enzyme they bind: the competitive inhibitors, which target the active site itself, and the non-competitive inhibitors, which bind somewhere else entirely.