How does enzyme concentration affect enzyme activity?

Enzyme activity is directly proportional to enzyme concentration but only up to a certain point. 

As the enzyme concentration increases, so does enzyme activity and reaction rate. This is because at higher enzyme concentrations, there are more enzyme molecules colliding with substrate molecules. However, this trend will continue only as long as there is substrate available to bind to. Once the enzymes have bound to all of the available substrate, the additional enzymes will not have anything to bind to and the enzyme activity will slow down or come to a halt.