Enzymes Classification and Activity Factors

Enzymes-2 Classification

• Enzymes are grouped into six major classes
• Oxidoreductases: These enzymes catalyze oxidation-reduction reactions, examples include dehydrogenases and oxidases.
• Transferases: Transfer functional groups (e.g., amino or phosphate groups) between donors and acceptors, examples include aminotransferases and kinases.
• Hydrolases: Hydrolases use water to catalyze the hydrolysis of substrates. Examples include proteases and phosphatases.
• Lyases: These enzymes add or remove the elements of water, ammonia, or carbon dioxide from or to double bonds. Examples include decarboxylases and synthases.
• Isomerases: These enzymes catalyze changes within one molecule. Mutases are an example.
• Ligases: These enzymes join two molecules together at the expense of ATP. Examples include synthetases and carboxylases.

Enzyme Activity Factors

• Substrate concentration: Increasing substrate concentration increases reaction velocity up to a point (Vmax). At Vmax, further substrate increases have no effect on velocity.
• Enzyme concentration: Increased enzyme concentration increases reaction velocity.
• pH: Enzyme activity is optimal at a specific pH. Deviations above or below the optimal pH decrease the reaction rate. Each enzyme has its own optimal pH.
• Temperature: Increasing temperature increases reaction velocity up to an optimum, after which, velocity decreases due to enzyme denaturation. Most enzymes denature at 55-60°C.

Measuring Enzyme Activity

• Decreasing substrate concentration
• Increasing product concentration

Reaction Velocity

• Reaction velocity is the substrate amount converted into product per time unit.
• Increasing substrate concentration increases reaction velocity.
• At Vmax, further substrate increases have no effect on velocity.

Km (Michaelis-Menten Constant)

• Km is the substrate concentration at half-maximum velocity.
• Km indicates the enzyme's affinity to the substrate.
• Low Km reflects high affinity and high Km reflects low affinity.

Enzyme Affinity

• Large Km values for an enzyme indicate low affinity
• Small Km values for an enzyme indicate high affinity