Overview
This lecture compares the four main types of enzyme inhibitors—competitive, non-competitive, mixed, and uncompetitive—focusing on their binding sites, effects on enzyme kinetics, and how to distinguish them on different plots.
Types of Enzyme Inhibitors
- Four types: competitive, non-competitive, mixed, uncompetitive.
- Enzymes lower activation energy, accelerate reactions, and are not consumed or altered by the reaction.
- Enzymes have an active site (front door) and an allosteric site (back door).
Competitive Inhibitors
- Bind only to the active site.
- Increase Km (decrease substrate affinity).
- Do not change Vmax (maximum reaction rate).
- Effects can be overcome by increasing substrate concentration.
- On Lineweaver-Burk plots, lines intersect at the y-axis.
Non-Competitive Inhibitors
- Bind to the allosteric site, not the active site.
- Do not change Km (affinity remains the same).
- Decrease Vmax.
- Cannot be overcome by adding more substrate.
- On Lineweaver-Burk plots, lines intersect at the x-axis.
Mixed Inhibitors
- Bind to the allosteric site, can bind to either the enzyme alone or the enzyme-substrate complex.
- Vmax always decreases.
- Km can either increase (decreased affinity) or decrease (increased affinity), depending on binding preference.
- On Lineweaver-Burk plots, lines intersect at a point not on either axis.
Uncompetitive Inhibitors
- Bind only to the enzyme-substrate complex at the allosteric site.
- Decrease both Km (increase affinity) and Vmax.
- Lines on Lineweaver-Burk plots are parallel.
Key Terms & Definitions
- Enzyme — Biological catalyst that speeds up reactions without being consumed.
- Active Site — Enzyme region where substrate binds.
- Allosteric Site — Site other than the active site where regulators or inhibitors bind.
- Km (Michaelis constant) — Inversely measures enzyme-substrate affinity.
- Vmax — Maximum rate of reaction when enzyme is saturated.
Action Items / Next Steps
- Review and memorize effects of each inhibitor type on Km and Vmax.
- Practice drawing Lineweaver-Burk and Michaelis-Menten plots for each inhibitor.
- Watch previous videos in the playlist for foundational understanding.