Enzymes

Enzyme action and kinetics

Enzymes are globular proteins that lower activation energy by forming enzyme–substrate complexes at a specific active site. Induced fit: the active site changes shape slightly as the substrate binds. Rate rises with temperature (more collisions) up to an optimum, then falls as bonds break and the enzyme denatures. Away from the optimum pH, ionic and hydrogen bonds change, altering the active site. Rate increases with substrate concentration until all active sites are occupied (Vmax). Km is the substrate concentration at ½Vmax: a low Km means high affinity. Competitive inhibitors bind the active site (overcome by more substrate; Vmax unchanged, Km increases). Non-competitive inhibitors bind elsewhere, changing the active site (Vmax decreases). Immobilised enzymes can be reused and give product free of enzyme.