Final Answer:
Noncompetitive or mixed inhibition results in a decrease in the maximum reaction velocity (Vmax) without affecting the Michaelis constant (Km).
Step-by-step explanation:
Noncompetitive inhibition occurs when the inhibitor binds to an allosteric site on the enzyme, distinct from the active site. This binding induces a conformational change in the enzyme structure, reducing its catalytic activity. As a result, the inhibitor and substrate can bind simultaneously, but the enzyme-substrate-inhibitor complex has reduced catalytic efficiency.
The Lineweaver-Burk plot, a graphical representation of enzyme kinetics, illustrates noncompetitive inhibition as converging lines on the y-axis. The intersection point on the y-axis represents the new Vmax, while the slopes remain constant, indicating unchanged Km. Mathematically, this is expressed as 1/Vmax = (Km/Vmax) × (1/[S]) + (1/Vmax).
Mixed inhibition shares similarities with noncompetitive inhibition but differs in the inhibitor's ability to bind to either the free enzyme or the enzyme-substrate complex. This dual binding results in an altered Vmax and an apparent change in Km. The Lineweaver-Burk plot for mixed inhibition displays intersecting lines away from the y-axis. The intersecting point provides the new Vmax and Km values, indicating the mixed nature of inhibition. In summary, non-competitive or mixed inhibition alters enzyme kinetics by modifying the maximum reaction velocity, a key parameter in enzyme catalysis.