Chemical Kinetics Practice Test 2026 – Your Comprehensive All-in-One Guide to Exam Success!

Inhibition type determines how Km and Vmax change. Competitive inhibitors resemble the substrate and compete for the active site, so you have to add more substrate to reach half-maximum velocity. That makes the apparent Km higher, while Vmax stays the same because, given enough substrate, the inhibitor can be outcompeted and the enzyme can reach the same maximal rate as without the inhibitor.

Noncompetitive inhibitors bind to a different site and can affect the enzyme regardless of whether the substrate is bound. This reduces the number of active catalytic centers, so the overall maximal rate drops (Vmax decreases). The substrate’s ability to bind the enzyme isn’t altered, so Km remains unchanged.

So, competitive inhibition raises Km with Vmax unchanged; noncompetitive inhibition lowers Vmax with Km unchanged.