Michaelis-Menton Equation and Product Inhibition

Enzyme Kinetics

• Enzyme kinetics are studied in enzyme assays, where an enzyme and substrate are mixed, and the loss of substrate or production of product is monitored.
• Various methods can be used to monitor enzyme kinetics, including absorbance, fluorescence, high-performance liquid chromatography (HPLC), and mass spectrometry.

Angiotensin I-Converting Enzyme

• Angiotensin I-converting enzyme is an example of an enzyme that is studied in enzyme assays.
• The enzyme converts angiotensin I to angiotensin II, which is a shorter, less hydrophobic fragment.

What is Enzyme Kinetics?

• Enzyme kinetics refers to the study of the rates of enzyme-catalyzed reactions.
• The rate of reaction is typically measured as the initial rate, which is the rate at which the product is formed at the beginning of the reaction.
• The initial rate is often dependent on the substrate concentration.

Rate of Reaction

• The rate of reaction is referred to as the velocity, V, and is usually expressed as µmol of product formed per minute (µmol/min).
• The specific activity of an enzyme is expressed as µmol of substrate converted per minute per mg of protein (µmol/min/mg protein).

Effect of Substrate Concentration on Enzyme Kinetics

• The effect of substrate concentration on enzyme kinetics can be studied by measuring the rate of reaction at different substrate concentrations.
• The initial rate is dependent on the substrate concentration, with the rate increasing as the substrate concentration increases.
• At high substrate concentrations, the rate of reaction reaches a maximum, known as Vmax.

The Michaelis-Menton Equation

• The Michaelis-Menton equation is a mathematical model that describes the kinetics of enzyme-catalyzed reactions.
• The equation is based on the assumption that the enzyme binds to the substrate to form an enzyme-substrate complex, which then breaks down to form the product.
• The equation can be used to derive the Michaelis constant, KM, which is the substrate concentration at which the rate of reaction is half of Vmax.

Derivation of the Michaelis-Menton Equation

• The derivation of the Michaelis-Menton equation involves several steps, including the assumption that the product does not revert to the substrate, and that the reaction is in a steady-state condition.
• The equation is derived by rearranging the equations to solve for [ES], the concentration of the enzyme-substrate complex.

Interpretation of the Michaelis-Menton Equation

• The Michaelis-Menton equation can be used to interpret the kinetics of enzyme-catalyzed reactions.
• The equation shows that the rate of reaction is dependent on the substrate concentration, with the rate increasing as the substrate concentration increases.
• The equation also shows that the rate of reaction reaches a maximum, Vmax, at high substrate concentrations.

Turnover Number

• The turnover number is the number of substrate molecules converted to product per enzyme molecule in unit time when the enzyme is saturated.
• The turnover number is a measure of the efficiency of an enzyme, with higher turnover numbers indicating more efficient enzymes.

Physiological Significance of KM

• The Michaelis constant, KM, has physiological significance, as it indicates the substrate concentration at which the enzyme is half-saturated.
• The KM value can be used to compare the activity of different enzymes, and to understand the regulation of enzyme-catalyzed reactions.

Isozymes

• Isozymes are enzymes that come from different genes, but perform identical reactions.
• Isozymes have slightly different amino acid sequences, which can affect their activity and substrate specificity.

Hexokinase Isozymes

• Hexokinase is an enzyme that catalyzes the conversion of glucose to glucose-6-phosphate.
• There are several isozymes of hexokinase, including hexokinase I, II, and III, and glucokinase (hexokinase IV).
• The different isozymes have different KM values, which can affect their activity and substrate specificity.

Physiological Significance of Hexokinase IV

• Hexokinase IV (glucokinase) has a higher KM value than the other hexokinase isozymes, which means it is less active at low glucose concentrations.
• Hexokinase IV is more active at high glucose concentrations, which is important for the regulation of glucose metabolism in the liver.

Effect of pH and Temperature on Enzyme Activity

• Enzymes are affected by pH, with many enzymes having an optimal pH for activity.
• Enzymes are also affected by temperature, with the rate of reaction increasing as the temperature increases, but decreasing after the optimal temperature.
• The effect of pH and temperature on enzyme activity can be used to understand the regulation of enzyme-catalyzed reactions.