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 V_max, 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 K_m without changing V_max.
• Noncompetitive: Bind allosteric site, lowering V_max without affecting K_m.
• Uncompetitive: Bind enzyme–substrate complex, decreasing both V_max and K_m.

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.