Rate: Inhibitor Concentration
- There are two types of inhibitors:
- Competitive inhibitors, which have a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site
- Non-competitive inhibitors, which bind to the enzyme at an alternative site, altering the shape of the active site and therefore preventing the substrate from binding to it
Enzyme Inhibitors Diagram
The two types of inhibitors, competitive and non-competitive, can affect the formation of enzyme-substrate complexes
- Both types of inhibitors slow down or stop enzyme activity
- Increasing the concentration of an inhibitor, therefore, reduces the rate of reaction and eventually, if inhibitor concentration continues to be increased, the reaction will stop completely
- For competitive inhibitors, countering the increase in inhibitor concentration by increasing the substrate concentration can increase the rate of reaction once more (more substrate molecules mean they are more likely to collide with enzymes and form enzyme-substrate complexes before the inhibitor can bind)
- For non-competitive inhibitors, increasing the substrate concentration cannot increase the rate of reaction once more, as the shape of the active site of the enzyme remains changed and enzyme-substrate complexes are still unable to form despite how many substrate molecules are present
Enzyme Inhibitor Graph
The effect of inhibitor concentration on the rate of an enzyme-catalysed reaction
Examiner Tip
While a competitive inhibitor will lower the initial rate of reaction (by occupying some of the available active sites), eventually the same amount of product will be produced as would have been produced without the competitive inhibitor (the maximal rate is not affected).
Non-competitive inhibitors lower the initial rate of reaction and the maximal rate of reaction (a lower amount of product is produced than would normally be produced).
