The effect of pH on enzyme activity: When the pH is too high or too low, the enzyme activity is significantly reduced Excessive acidity or alkalinity can denature and inactivate the enzyme itself; ② Changes in pH can affect the dissociation of relevant functional groups on the active site of enzyme molecules; ③ PH can affect the dissociation of substrates.

① Excessive acidity or alkalinity can denature and inactivate the enzyme itself

② Changes in pH can affect the dissociation of relevant functional groups on the active site of enzyme molecules. At the optimal pH, the dissociation state of the active group on the enzyme molecule is most suitable for binding to the substrate. When the pH is higher or lower than the optimal pH, the dissociation state of the active group changes, and the binding force between the enzyme and the substrate decreases, resulting in a decrease in the enzyme reaction rate.

③ PH can affect the dissociation of substrates. It can be imagined that certain functional groups on the substrate molecule are only suitable for reacting with enzymes in a certain dissociation state. If the change in pH affects the dissociation of these groups, making them unsuitable for enzyme binding, the reaction rate will also slow down.

The enzyme, which is essentially a protein, is affected by physical or chemical factors, causing changes in its highly regular structure within the molecule. Secondary bonds (such as hydrogen bonds, salt bonds, hydrophobic bonds, van der Waals forces, etc.) are disrupted, and protein molecules change from an orderly coiled and tightly packed structure to an disordered and loosely stretched structure. This means that higher structures above the second and third levels are disrupted, but the primary structure formed by covalent bonds (such as peptide bonds and disulfide bonds) is not disrupted. The biological function of denatured proteins is lost. However, the denaturation of proteins, if not too drastic and the internal structure of protein molecules does not change significantly, is a reversible reaction. For example, when gastric protease is heated to 80-90 ℃, it has no ability to digest proteins. If the temperature is further reduced to 37 ℃, it can restore its ability to digest proteins. But as the denaturation time increases, the conditions worsen and the degree of denaturation deepens, making it impossible to achieve reversible denaturation.