5. Regulation of the enzyme activity. Regulation by altering the absolute amount of the enzyme. Regulation by altering the activity of the enzyme – proenzymes, reversible covalent modification, allosteric regulation, etc.

Effect of pH and Temperature on Enzyme-Catalyzed Reactions

Temperature

• Increase of velocity with temperature:
• Increases until a peak is reached.
• Increased number of molecules have sufficient energy to overcome the energy barrier and form reaction products.
• Decrease of velocity at higher temperatures:
• Temperature-induced denaturation of the enzyme.
• The optimum temperature for most human enzymes is 35 to 40 degrees Celsius, beyond which they denature.

pH

• Effect of pH on the ionization of the active site:
• The active site's amino acid residues can exist in different ionization states depending on the pH, affecting substrate binding and catalysis.
• Enzyme stability and activity are influenced by pH, with optimal ranges for maximum activity.
• Effect of pH on enzyme denaturation:
• Extremely high or low pH levels can denature enzymes, altering their structure and function.
• Optimum pH varies for different enzymes:
• Each enzyme has a specific pH range for optimal activity; for example, pepsin operates best at pH 2.
• Changes in pH optimum due to high ethanol sensitivity:
• In high ethanol sensitivity, the pH optimum for alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) can shift, affecting ethanol metabolism.