Biochemistry: Factors Affecting Reaction Velocity - Enzymes Part 2

Enzyme Kinetics and Temperature

• Reaction velocity generally increases with temperature due to enhanced molecular collisions but can decrease at extreme temperatures due to denaturation.

Substrate Concentration and Reaction Velocity

• Higher substrate concentration increases enzyme reaction velocity until a saturation point is reached, beyond which the velocity remains constant.

Irreversible Inhibitors

• An irreversible inhibitor covalently binds to an enzyme, permanently deactivating its activity.

Noncompetitive Inhibition

• Noncompetitive inhibition reduces enzyme activity regardless of substrate concentration by binding to an allosteric site, affecting Vmax without changing Km.

Michaelis-Menten Constant (Km)

• Km reflects the substrate concentration at which an enzyme operates at half its maximum velocity (Vmax), indicative of enzyme affinity for the substrate.

Low Km Value Impact

• A low Km indicates a high affinity between enzyme and substrate, leading to effective enzyme-substrate reactions at lower substrate concentrations.

Reaction Velocity at Substrate Concentration < Km

• When substrate concentration is below Km, reaction velocity is directly proportional to substrate concentration, exhibiting first-order kinetics.

Vmax Change and Inhibition

• Noncompetitive inhibition results in a decrease of Vmax, but Km remains unchanged.

pH Effects on Enzyme Activity

• Enzyme activity is highly dependent on pH, with optimal ranges for activity specific to each enzyme; extreme pH levels can lead to denaturation.

Michaelis-Menten Equation

• The Michaelis-Menten equation mathematically describes the rate of enzymatic reactions as a function of substrate concentration.

Main Assumption of Michaelis-Menten Kinetics

• Assumes that the formation of the enzyme-substrate complex is at a steady state and that the breakdown of this complex is the rate-limiting step.

Vmax Definition

• Vmax represents the maximum rate of enzymatic reaction when the enzyme is fully saturated with substrate.

Competitive Inhibition Mechanism

• Competitive inhibitors bind to the active site of the enzyme, blocking substrate access and increasing the apparent Km.

Zero Order Kinetics and Substrate Concentration

• In zero-order kinetics, when substrate concentration exceeds Km, the reaction velocity becomes constant and is independent of substrate concentration.

Vmax and Noncompetitive Inhibition

• Increasing substrate concentration does not reverse the Vmax reduction caused by noncompetitive inhibitors because the inhibitor affects enzyme functionality regardless of substrate levels.

Hyperbolic Curve in Michaelis-Menten Kinetics

• Enzymes following Michaelis-Menten kinetics display a hyperbolic curve when plotting reaction velocity versus substrate concentration.

Allosteric Enzyme Kinetics

• Allosteric enzymes exhibit sigmoidal curves, indicating cooperative binding, as opposed to hyperbolic curves of typical Michaelis-Menten kinetics.

Statin Drugs as Competitive Inhibitors

• Statin drugs competitively inhibit HMG-CoA reductase, reducing cholesterol synthesis by mimicking the natural substrate.

Lineweaver-Burk Plot for Vmax

• Vmax can be determined from the y-intercept of a Lineweaver-Burk plot, which is a double reciprocal graph of reaction velocity versus substrate concentration.

β-lactam Antibiotics Action

• β-lactam antibiotics, like penicillin, inhibit bacterial cell wall synthesis by targeting and inactivating transpeptidase enzymes.

Purpose of Reciprocal Plotting

• Plotting 1/v0 versus 1/[S] facilitates linearization of enzyme kinetics data, simplifying the calculation of Vmax and Km.

Aspirin's Effect on Synthesis

• Aspirin inhibits the cyclooxygenase enzyme, reducing the synthesis of prostaglandins and thromboxanes involved in inflammation and pain.

Competitive Inhibition and Km

• The presence of a competitive inhibitor increases the apparent Km for a given substrate, indicating decreased affinity.

Competitive vs. Noncompetitive Inhibitors

• Competitive inhibitors bind to the active site while noncompetitive inhibitors bind to an allosteric site, affecting enzyme activity differently.

Lineweaver-Burk Plot and Competitive Inhibition

• In competitive inhibition, the presence of an inhibitor increases the slope of the Lineweaver-Burk plot but keeps the y-intercept (1/Vmax) constant.

Noncompetitive Inhibitor Effects

• Noncompetitive inhibitors reduce enzyme activity irrespective of substrate concentration, lowering Vmax without affecting Km.

Primary Effects of Noncompetitive Inhibitors

• They lower the maximum reaction velocity (Vmax) without altering the affinity (Km) for the substrate.

Competitive Inhibition Characteristics

• Competitive inhibition can be outcompeted by increasing substrate concentration, allowing enzymes to reach normal activity.

Distinguishing Features of Noncompetitive Inhibition

• Noncompetitive inhibitors bind to sites other than the active site and do not compete with substrates, leading to decreased enzyme efficiency.

Explore how enzymes function in living cells through in vitro studies. Learn about the impact of substrate concentration on enzyme-catalyzed reactions, including the concept of Vmax and saturation. Discover the influence of temperature and pH on enzyme activity.