Now, property number five of enzymes and the active sides of enzymes is that active sites typically bind substrates reversibly via non covalent forces. So in property number one and two, we basically mentioned that inside the active side we have these special residues, the amino acids that contain the special side chain groups that are responsible for actually attaching and binding the substrate molecules. And the binding that takes place takes place via non covalent interactions such as hydrogen bonds, such as hydrophobic interactions and vandervals forces. So non covalent electric forces such as hydrogen bonds, Vanderwal's forces and the hydrophobic effect can all promote the reversible binding between the active side and the substrate. And what reversible binding basically means is once the substrate binds onto that active side and once we convert the substrate to the product, that product will essentially release itself and move away from the active site, it will not remain bound to that active site forever. That's what we mean by reversible binding.