The ability of the enzyme to perform its function depends on its active site. The active site is formed by the residues of amino acids in such a way that it can bind to a molecule of a particular composition and shape. This mode of action is called the lock-and-key model.
- At present, there is another model that is called “induced fit model“. According to that idea, the enzyme reacts to the nearness of the correct molecule (called a substrate) and shapes its active site so the substrate would fit fully into it.
- The active site may have one or more “landing points” for molecules. This way, the enzyme can bring two molecules together so that they can react with each other.
If those molecules were just placed in the solution, they would react much slower. It happens for several reasons:
- First of all, each reaction requires a certain amount of energy. When the enzyme binds to the molecules participating in the reaction, it also lowers the amount of energy that would be required.
- During each reaction, the potential result product has to go through the so-called transition state. It is very unstable. However, when the molecules are bound to the enzyme, this transitional product is much more stable so that the reaction can go faster.
- The enzyme also weakens the bonds between the components of the molecule, so that it can be broken up or new parts can be attached to it.
When the reaction is finished, the products no longer fit into the active site of the enzyme, so they are released. Another molecule can take its place, and the whole process can begin again.
Inhibitors that can block the enzymes have similar shapes to the “correct” molecules, but they bind to the active site in the slightly wrong way so that the specific activity of this particular protein (for example, ability to attach chemical groups) is blocked.
