Factors Affecting Enzyme Action

Concentration of Substrate and Reaction Rate

• Initial velocity of a reaction is directly proportional to substrate concentration until reaching maximum velocity (Vmax).
• Beyond Vmax, further substrate increases do not affect reaction velocity when enzyme concentration remains constant.
• Reaction rate is the amount of substrate converted to product per unit time, commonly expressed as micromoles of product formed per minute.
• Reaction rate increases with substrate concentration until all enzyme binding sites are saturated.

Factors Affecting Enzyme Action

• Enzyme responses vary with substrate concentration, temperature, and pH levels.
• At low temperatures, enzyme activity is minimal; activity increases with temperature until an optimal peak is reached (typically around 37°C in humans).
• High temperatures can lead to denaturation of enzymes, reducing reaction velocity.

Enzyme Characteristics

• Enzymes are catalysts that accelerate reaction rates without being consumed; they are proteins with high specificity.
• They affect the rate of reaction but not the overall equilibrium.
• Enzymes can require cofactors or coenzymes and participate in various biochemical pathways.

Active Site and Mechanism of Action

• The active site is the enzyme region that binds substrates, forming an enzyme-substrate complex through weak non-covalent interactions.
• Activation energy is the energy needed for substrates to reach the transition state; enzymes lower this energy barrier.
• Specificity of enzymes is determined by both substrate and enzyme functional groups and their spatial arrangement.

Enzyme Kinetics

• Enzyme kinetics studies reaction velocity, defined as the rate of product formation or substrate consumption over time.
• Initial velocity (Vi) is measured during the first portion of the reaction, correlating product increase with time.
• Factors affecting enzyme activity include enzyme concentration, with initial velocity proportionate to enzyme amount, independent of substrate concentration parameters such as Km.

Michaelis-Menten Kinetics

• The relation between reaction velocity (V) and substrate concentration ([S]) can be described by the Michaelis-Menten equation.
• When [S] exceeds Km, the reaction rate reaches Vmax, indicating a zero-order reaction.
• The Lineweaver-Burk Plot provides a linear transformation of the Michaelis-Menten equation, allowing easy determination of Vmax and Km from graph intercepts.

Enzyme Inhibition

• Enzyme inhibitors reduce reaction velocity and catalytic activity; can be reversible or irreversible.
• Competitive inhibitors resemble substrate and compete for the active site, increasing the apparent Km but not affecting Vmax.
• Noncompetitive inhibitors bind at a site separate from the substrate, reducing Vmax without affecting Km.

Enzyme Inhibitors in Medicine

• Sarin is a nerve gas that inhibits acetylcholinesterase, preventing acetylcholine hydrolysis, leading to excessive neuronal stimulation and severe physiological effects.
• Penicillin acts as an antibiotic by inhibiting bacterial peptidoglycan synthesis, preventing cell wall formation and bacterial growth.