So previously in our discussion of the Michaelis constant, we said that the Michaelis constant represents the concentration of the substrate at which the enzymes activity. The enzymes rate is exactly half of its maximum rate. So the Km describes the substrate concentration that is needed to reach exactly half of that maximum velocity of that particular enzyme. And what that basically means is when our substrate concentration is equal to Km, exactly half of all the active sites in the enzyme mixture are filled with the substrate. And this can be seen in the following diagram. So initially we begin with, let's say, an enzyme mixture that consists of four identical enzymes.