Summary
An inhibitor binds elsewhere on the enzyme, lowering Vmax without changing Km.
In depth
The inhibitor binds to a site other than the active site on either the free enzyme or the enzyme-substrate complex, changing its shape and reducing catalytic efficiency. Adding more substrate cannot fix it, so Vmax falls while Km is unchanged.
Heavy metals such as lead and mercury often act this way.
On Lineweaver-Burk plots, noncompetitive inhibitors lower Vmax but leave Km unchanged, since they reduce the amount of functional enzyme without altering substrate binding. Uncompetitive inhibitors bind only the enzyme-substrate complex and lower both.
Irreversible inhibitors, which bind covalently, are a different class: aspirin acetylates cyclooxygenase, penicillin binds transpeptidase, and nerve agents inhibit acetylcholinesterase. Heavy metals can inhibit noncompetitively by binding to sulfhydryl groups.
Common mistake: assuming that adding more substrate always overcomes inhibition; this is true only for competitive inhibitors.
Frequently asked questions
What is Noncompetitive Inhibition?
An inhibitor binds elsewhere on the enzyme, lowering Vmax without changing Km.
Which area of biology covers Noncompetitive Inhibition, and how advanced is it?
Noncompetitive Inhibition is one of the 51 topics in Biomolecules & Biochemistry. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Competitive Inhibition, Michaelis-Menten Kinetics, Cofactors and Coenzymes.
Can you give an example of Noncompetitive Inhibition?
Cyanide binds cytochrome c oxidase and blocks respiration.
What should I learn before Noncompetitive Inhibition?
Work through the Beginner topics in Biomolecules & Biochemistry first, such as Water Properties, Carbon Chemistry, Carbohydrates, then return to Noncompetitive Inhibition. Advanced topics assume the Intermediate vocabulary.
What topics are related to Noncompetitive Inhibition?
The closest topics to Noncompetitive Inhibition are Competitive Inhibition, Michaelis-Menten Kinetics, Cofactors and Coenzymes, Induced Fit Model. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Noncompetitive Inhibition?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Noncompetitive Inhibition. To practise the whole of Biomolecules & Biochemistry, use the Biomolecules & Biochemistry quiz.
How is Noncompetitive Inhibition different from Competitive Inhibition?
Noncompetitive Inhibition: An inhibitor binds elsewhere on the enzyme, lowering Vmax without changing Km. Competitive Inhibition: An inhibitor resembling the substrate binds the active site and can be overcome by more substrate. Read both side by side and note what each one explains.
What is a common mistake about Noncompetitive Inhibition?
Assuming that adding more substrate always overcomes inhibition; this is true only for competitive inhibitors.
How should I study Noncompetitive Inhibition step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Competitive Inhibition and explain the difference aloud. Finally, take the Biomolecules & Biochemistry quiz and come back to this page for any question you miss.