Models of Action

There are two models used to describe the way enzymes interact with substrates:

  • The 'lock and key’ model
  • The ‘induced fit’ model

The Lock and Key Model

According to the lock and key model, the enzyme’s active site complements the substrate precisely

The substrate fits a particular active site like a key fits into a particular lock

This theory of enzyme-substrate interaction explains how enzymes exhibit specificity for a particular substrate

The Induced Fit Model

According to the induced fit model, the enzyme’s active site is not a completely rigid fit for the substrate

Instead, the active site will undergo a conformational change when exposed to a substrate to improve binding

This theory of enzyme-substrate interactions has two advantages compared to the lock and key model:

  • It explains how enzymes may exhibit broad specificity (e.g. lipase can bind to a variety of lipids)
  • It explains how catalysis may occur (the conformational change stresses bonds in the substrate, increasing reactivity)