Factors Affecting Enzyme Activity

Factors Affecting Enzyme Activity

• The following factors affect enzyme activity:
  • Substrate concentration
  • Enzyme concentration
  • pH (H+ ion concentration)
  • Temperature
  • Product concentration
  • Activators and coenzymes
  • Time
  • Physical agents
  • Inhibitors

Effect of Substrate Concentration

• The velocity of the reaction increases with increasing substrate concentration, but eventually reaches a plateau (Vmax)
• At low substrate concentrations, the reaction follows first-order kinetics (V0 increases linearly with substrate concentration)
• At high substrate concentrations, the reaction follows zero-order kinetics (V0 increases by smaller amounts with increasing substrate concentration)
• Km is the Michaelis-Menten constant, which represents the substrate concentration at which the reaction rate is half of Vmax

Effect of Enzyme Concentration

• The velocity of the reaction is directly proportional to the amount of enzyme present, as long as the substrate is not limiting
• The substrate must be present at a concentration sufficient to ensure that all enzyme molecules have substrate bound to their active site

Effect of pH (H+ ion concentration)

• Each enzyme has an optimum pH, at which the enzyme activity is maximum
• Below or above this pH, enzyme activity is decreased
• Optimum pH differs from enzyme to enzyme (e.g., pepsin: 1.2, trypsin: 8.0)
• Changes in pH can alter the ionization state of the amino acid residues in the active site and the substrate

Effect of Temperature

• Enzyme-catalyzed reactions show an increase in rate with increasing temperature, but only within a relatively small and low temperature range
• Each enzyme has an optimum temperature, at which the activity is highest
• The activity progressively declines both above and below this temperature
• Increase in velocity is due to the increase in kinetic energy; further elevation of temperature results in denaturation of the enzyme protein

Effect of Product Accumulation

• Accumulation of products can cause inhibition of enzyme activity for some reactions
• In biological systems, the product is usually removed as it becomes a substrate for a succeeding enzyme in a metabolic pathway

Effect of Activators and Coenzymes

• The activity of many enzymes is dependent on activators (metallic ions) and coenzymes for their optimum activity
• In the absence of these activators and coenzymes, enzymes become functionally inactive

Effect of Time

• Under optimum conditions of pH and temperature, the time required for an enzyme reaction is less
• The time required for the completion of an enzyme reaction increases with changes in temperature and pH from its optimum

Effect of Physical Agents

• Physical agents like light rays can inhibit or accelerate certain enzyme reactions
• For example, the activity of salivary amylase is increased by red and blue light and inhibited by ultraviolet rays

Effect of Inhibitors

• Inhibitors are substances that stop the enzymatic reaction
• Presence of these substances in the reaction medium decreases the rate of enzyme reaction
• Different types of enzyme inhibitors will be discussed separately later

Enzyme Inhibitors

• Enzyme inhibitors are useful in elucidating cellular metabolic pathways and studying metabolic pathways.
• They provide information about substrate specificity of enzymes.
• They are useful for understanding the regulation of enzyme activity within living cells.
• They help in identifying catalytic/functional groups at the active site of enzymes.

Applications of Enzyme Inhibitors in Medicine

Medical Device Cleaning

• Enzymatic detergents are used to clean reusable medical devices.
• Protease and lipase are the two main enzymes used for cleaning medical devices.
• Other enzymes used are amylases and cellulases.

Treatment of Disorders

• Enzymes are used to break internal blood clots, dissolve hardening of blood vessel walls, and promote wound healing.
• Enzymes like serratiopeptidase, trypsin, and chymotrypsin are used to dissolve wound swelling.

Assisting Metabolism

• Enzymes like papain are administered orally to aid digestion in patients with low digestive capacity.

Mechanism-Based Inactivation

• Suicide inhibitors or mechanism-based inactivators are compounds that bind to the active site of an enzyme and permanently block it.
• Examples of mechanism-based inactivators include penicillin, aspirin, and disulfiram.

Clinical Applications of Enzyme Inhibitors

• Enzyme inhibitors have therapeutic applications, and most antibiotics and anticancer drugs are either competitive inhibitors or mechanism-based suicide inhibitors.

Enzymes in Drug Delivery

• Enzymes like hyaluronidase are used to assist drug delivery to the target site.

Enzymes in Diagnosing Disorders

• Enzymes can be used as biomarkers to diagnose disorders, such as creatine kinase for muscle and heart weakness and injury.

Enzymes in Manufacturing Medicines

• Immobilized enzymes are used in the manufacture of many drugs and antibiotics.
• Examples of enzymes used in manufacturing include alpha amylase, lipase, asparaginase, protease, and streptokinase.

Enzymes in Toothpaste

• Enzymes like papain and glucose oxidase are used in toothpaste to remove stains and give white and sparkling teeth.