Usually a very small amount of enzyme can consume a large amount of substrate. The rate of reaction depends directly on the amount of enzyme present at a specific time at unlimited substrate concentration. If two folds increase the amount of enzyme the reaction rate is doubled.
By increasing the enzyme molecules an increase is the number of active sites takes place.
At higher concentration of the enzyme the inhibitors will fall short. More active sites will convert the substrate molecules into products, in the given period of time. After a certain limiting concentration, the rate of reaction will no longer depend upon this increase.
At low concentration of substrate the reaction rate is directly proportional to the substrate available.If the enzyme concentration is kept constant and the amount of substrate is increased, a point is reached when a further increase in the substrate does not increase the rate of the reaction any more. This is because at high substrate level all the active sites of the enzyme are saturated with substrate. After this, the rate of enzyme reaction becomes steady and addition of the substrate will not have the positive effect.