Enzyme kinetics is the study of the rates at which enzymes catalyze biochemical reactions. By measuring how reaction velocity changes with substrate concentration, scientists can determine key parameters that describe an enzyme’s activity and efficiency.

Key Concepts in Enzyme Kinetics

Reaction Velocity

The velocity of an enzyme-catalyzed reaction is measured as the amount of product formed per unit time. Initial velocity (V0) is measured at the beginning of the reaction when substrate concentration is much higher than product concentration.

Michaelis-Menten Equation

The Michaelis-Menten model describes the relationship between substrate concentration [S] and reaction velocity V:

V = Vmax × [S] / (Km + [S])

Vmax is the maximum velocity when the enzyme is saturated with substrate. Km (the Michaelis constant) is the substrate concentration at which the reaction rate is half of Vmax. It reflects the enzyme’s affinity for its substrate: a low Km means high affinity.

Michaelis-Menten Plot

When velocity is plotted against substrate concentration, the resulting curve is a hyperbola. At low substrate concentrations, velocity increases linearly. As substrate concentration increases, the curve approaches Vmax asymptotically.

Lineweaver-Burk Plot

The Lineweaver-Burk plot linearizes the Michaelis-Menten equation by taking the reciprocal of both sides:

1/V = (Km/Vmax) × 1/[S] + 1/Vmax

The x-intercept is -1/Km, and the y-intercept is 1/Vmax. This plot is useful for determining kinetic parameters and identifying types of enzyme inhibition.

Turnover Number (kcat)

The turnover number kcat represents the number of substrate molecules converted to product per enzyme molecule per second. It is calculated as kcat = Vmax / [E]total. The ratio kcat/Km measures catalytic efficiency.