Enzymes accelerate reactions by binding substrate at an active site, forming an enzyme-substrate complex that breaks down into product plus free enzyme. The Michaelis-Menten equation describes how reaction speed saturates as substrate increases.
E + S ⇌ ES → E + P
v = (Vmax · [S]) / (Km + [S])
Vmax = k_cat · [E]_total
- Substrate [S] — number of substrate molecules (purple) diffusing in the vessel; more substrate raises velocity until saturation.
- Enzyme sites [E] — number of active sites (gold, fixed in a lattice) available to bind substrate.
- Affinity (1/Km) — how easily substrate binds once nearby; higher affinity means a smaller Km and faster saturation.
- Catalytic rate k_cat — how quickly a bound complex converts to product once formed.
This exact framework underlies drug design (most enzyme-inhibiting drugs work by changing effective Km or Vmax) and diagnostic blood tests that measure enzyme activity to detect disease.