Factors Affecting the rate of Enzymes
Factors Affecting the Rate of Enzymes
Overview of Enzyme Rate
The rate of an enzyme‑catalyzed reaction depends on how fast substrate molecules are converted to product. Key parameters include:
- Activation energy lowering by the enzyme
- Frequency of productive enzyme–substrate collisions
- Stability of the enzyme’s active conformation
Effect of Temperature
Increase Phase: Higher temperatures raise kinetic energy, increasing collision frequency and reaction rate.
Optimum: Each enzyme has an optimal temperature at which activity peaks.
Denaturation: Excessive heat disrupts tertiary structure, reducing activity.
Effect of pH
pH affects ionizable side chains in the active site:
- Optimal pH: Specific to each enzyme based on its natural environment.
- Extremes: High or low pH can denature the enzyme or alter charge interactions, reducing activity.
Substrate Concentration
At low [S], rate increases nearly linearly with substrate. As [S] approaches saturation, the rate nears Vmax, where all active sites are occupied.
Enzyme Concentration
Under constant substrate conditions, increasing enzyme concentration increases reaction rate proportionally, until other factors become limiting.
Inhibitors
- Competitive: Bind active site, raising apparent Km without changing Vmax.
- Noncompetitive: Bind allosteric site, lowering Vmax without affecting Km.
- Uncompetitive: Bind enzyme–substrate complex, decreasing both Vmax and Km.
Activators & Cofactors
Cofactors: Inorganic ions or metal ions (e.g., Mg²⁺, Zn²⁺) essential for enzyme structure or function.
Coenzymes: Organic molecules (e.g., NAD⁺, FAD) that shuttle electrons or groups between enzymes.
Allosteric Activators: Molecules that increase activity by stabilizing the active conformation.