But if we decrease or increase our PH the activity of those enzymes will drop as shown by these decreasing slopes. Now, the final factor that we want to discuss is the concentration of the substrate. So let's suppose that we begin with a relatively small quantity of substrate as well as some fixed amount of our enzyme. And this basically means that initially most of our active sites on our enzymes are actually empty. Now, as we begin to increase the amount of substrate as we begin to increase the concentration of our substrate more and more of the active sites will be occupied, will be filled and that will increase the overall rate of our reaction. Eventually, however, we will reach a point at which all the active sites on all our enzymes are filled.