A number of external factors can influence the activity of enzymes and, therefore, the rate of biological reactions. These include substrate concentration, enzyme concentration, temperature and pH.
There are two key points to remember when explaining these influences:
- enzyme molecules need to collide with substrate molecules, so factors that influence the chance of collision, such as the substrate concentration and temperature, influence the rate of reaction.
- enzymes are globular proteins with a precise tertiary structure, so factors that influence the protein shape or the binding of the substrate, such as high temperature and pH, influence the rate of reaction
The effect of substrate concentration on enzyme actvity
- At low substrate concentrations, an increase in concentration increases the enzyme activity. This is because a greater concentration of substrate molecules increases the chances of collision with enzyme molecules. Therefore, more enzyme-substrate complexes formed.
- At high substrate concentrations, an increase in concentration does not cause a further increase in activity. This is because at high substrate concentrations the enzymes are fully employed and so, at any one moment, all the active sites are occupied.