Substrate concentration
Increasing the concentration of the substrate increases the rate of reaction until the enzymes become saturated – this means that they are working at full capacity. Then, the rate of reaction plateaus unless more enzymes are added to the substrate. However, increasing the substrate concentration does not affect the rate of reaction when the enzymes are saturated. This is because the point of saturation has been reached.
Enzyme concentration
All the time the substrate is in excess, increasing the concentration of the enzyme will increase the rate of reaction.