Increasing the enzyme concentration as long as substrate concentration is optimum will increase the rate of reaction.
Step-by-step explanation:
If in a reaction the enzyme is operating at optimum temperature and pH and has been saturated with substrate the only option will be is to increase the enzyme concentration to increase the rate of reaction.
Sometimes allosteric activators can also be used in the reaction but increasing enzyme concentration is more appropriate as long as the optimum substrate level is there.