How does enzyme concentration affect reaction rates?

Enzyme concentration directly affects the rate of an enzyme-catalyzed reaction. Here’s how:

1. At low enzyme concentration:
   • There are fewer enzyme molecules available to bind with substrate molecules.
   • The reaction rate is slow, because not all substrate molecules can form enzyme–substrate complexes.
2. As enzyme concentration increases:
   • More enzyme molecules are available, so more enzyme–substrate complexes can form.
   • The reaction rate increases proportionally to the enzyme concentration (as long as substrate is in excess).
3. At very high enzyme concentration:
   • If the substrate concentration becomes the limiting factor, all substrate molecules are already bound.
   • Increasing enzyme concentration no longer increases the reaction rate — the rate reaches a maximum (plateau).

In short:

• Low enzyme → slow reaction
• Moderate enzyme → faster reaction
• High enzyme + limited substrate → no further increase in rate

So, enzyme concentration affects reaction rate only up to the point where substrate becomes limiting.