Biology – Factors that affect enzyme action | e-Consult

Enzymes are biological catalysts that speed up biochemical reactions. Their activity can be regulated by inhibitors, which are molecules that reduce enzyme activity. Inhibitors can be broadly classified as reversible and irreversible. This question focuses on reversible inhibitors, specifically competitive and non-competitive.

Competitive Inhibitors: Competitive inhibitors are molecules that resemble the substrate and bind to the active site of the enzyme. This binding prevents the substrate from binding, effectively blocking the catalytic site. The effect of a competitive inhibitor is a decrease in the reaction rate. The degree of inhibition is dependent on the concentration of the competitive inhibitor. Increasing the substrate concentration can overcome the effect of a competitive inhibitor; at sufficiently high substrate concentrations, the enzyme can become saturated with substrate, outcompeting the inhibitor. The Km (Michaelis constant) of the enzyme appears to be unaffected by a competitive inhibitor, as the inhibitor simply makes it harder for the substrate to bind, not that the enzyme's affinity for the substrate has changed. The Vmax (maximum reaction rate) remains the same, as with sufficient substrate, the enzyme can still achieve its maximum catalytic rate.

Non-Competitive Inhibitors: Non-competitive inhibitors bind to a site on the enzyme that is distinct from the active site. This binding causes a conformational change in the enzyme, which reduces its catalytic activity. Unlike competitive inhibitors, non-competitive inhibitors do not directly compete with the substrate for the active site. The effect of a non-competitive inhibitor is also a decrease in the reaction rate. However, unlike competitive inhibitors, increasing the substrate concentration cannot overcome the effect of a non-competitive inhibitor. This is because the inhibitor affects the enzyme's ability to catalyze the reaction, regardless of substrate concentration. The Km (Michaelis constant) appears to be unchanged by a non-competitive inhibitor. However, the Vmax (maximum reaction rate) is reduced because the inhibitor prevents the enzyme from achieving its full catalytic potential.

Diagram:

A diagram should show:

• The enzyme with its active site.
• The substrate binding to the active site, forming the ES complex.
• The competitive inhibitor binding to the active site, preventing substrate binding.
• The non-competitive inhibitor binding to a site other than the active site, causing a conformational change in the enzyme.
• A graph showing the effect of increasing inhibitor concentration on reaction rate, demonstrating the decrease in rate with both types of inhibitors.