Boiling enzymes raises their temperature, which increases the rate of activity of the enzymes. However, there is a limit beyond which enzymes stop working and become denatured. Too much heat breaks the chemical bonds that hold the enzymes together.
Increasing temperature increases collision between substrate molecules and water molecules. The speed of random molecular motion and vibration energy of molecules increases with an increase in temperature. Enzymes consist of individual amino acids joined together in a three-dimensional structure by chemical bonds between amino acids. When temperatures increase beyond an upper limit, the enzymes lose the three-dimensional structure, which makes them unable to fit their target substrate molecules.
Consequently, the enzymes become denatured and stop working. This is an irreversible process, and lowering the temperature does not restore the functions of the enzymes. On the other hand, low temperatures slow the enzymes' activities. At freezing point, molecular motion decreases considerably because solid formation occurs, causing molecules to lock into a rigid crystalline structure.
Enzymes are three-dimensional proteins that catalyze chemical reactions. Without enzymes, some reactions would otherwise not take place or would be too slow to support life. In other words, enzymes facilitate the formation or breaking of atomic bonds. The rate at which enzymes affect their respective reactions and the ability to retain their structure largely depend on temperature.