This three dimensional crevice, the three dimensional crack in that enzyme is the active side. And this active side consists of the residues, those amino acids that are responsible for binding onto the substrate. And not only that, inside the active side, we also have these catalytic groups, these residues part of the enzyme that are responsible for actually catalyzing that particular reaction. And this leads us directly into property number two. Active sites are responsible for stabilizing the transition state as well as forming and breaking the particular bonds involved in that chemical biological reaction. So inside the active side, we have those residues responsible for actually stabilizing and lowering the energy of the transition state.