So the Y axis is the enzyme activity, also called the enzyme velocity. And the X axis is the substrate concentration. So basically, this dashed line represents the maximum velocity at which that enzyme or the mixture of enzymes will actually operate. And notice we have this line and this curve will never actually cross this line. It will never actually go higher than the line because if we have, for example, 100 enzymes, we only have 100 possible active sites. So even if we have, let's say, 200 substrate molecules because we have an excess of substrate molecules and only 100 active sites, we have a maximum activity at which only 100 active sites at a time can actually be filled.