Enzyme Kinetics Calculator (Michaelis-Menten)

Enzyme Kinetics Guide

What do I need to know about Michaelis-Menten Equation?

V = Vmax × [S] / (Km + [S]). Where V = reaction velocity (rate), Vmax = maximum velocity at saturating substrate, [S] = substrate concentration, Km = Michaelis constant (substrate concentration at half Vmax). When [S] = Km: V = Vmax/2 (half maximum velocity). When [S] << Km: V ≈ (Vmax/Km) × [S] (first-order kinetics — rate proportional to [S]). When [S] >> Km: V ≈ Vmax (zero-order kinetics — rate independent of [S], enzyme is saturated). Km is a measure of enzyme-substrate affinity — low Km means the enzyme reaches half-maximal velocity at a low substrate concentration, indicating high affinity — it binds and processes the substrate efficiently even when there's relatively little of it around. A high Km indicates the enzyme needs a much higher substrate concentration before it works efficiently, i.e. lower affinity.

What do I need to know about Lineweaver-Burk Plot?

Taking reciprocals of the Michaelis-Menten equation: 1/V = (Km/Vmax) × (1/[S]) + 1/Vmax. This is a straight line (y = mx + c): x-axis: 1/[S], y-axis: 1/V. y-intercept: 1/Vmax (x = 0). x-intercept: −1/Km (y = 0). Gradient: Km/Vmax. Used to determine Km and Vmax from experimental data. Limitation: data points at high [S] (low 1/[S]) cluster near the origin and have more influence — errors in these measurements are amplified. The Eadie-Hofstee and Hanes-Woolf plots are more statistically robust alternatives, since they don't compress the high-concentration data points the way the double-reciprocal transformation does — modern enzyme kinetics work typically fits the untransformed Michaelis-Menten curve directly using non-linear regression software rather than relying on any of the linearised plots, which are now used mainly for teaching the underlying relationships.

What's the key thing to understand about Enzyme Inhibition Types?

Competitive inhibition: inhibitor competes with substrate for the active site. Increases apparent Km (reduced affinity). Vmax unchanged. On Lineweaver-Burk: lines intersect at y-axis (same 1/Vmax, changed 1/[S] intercept). Example: malonate inhibiting succinate dehydrogenase. Non-competitive inhibition: inhibitor binds elsewhere, reducing Vmax but not Km. Lines intersect at x-axis (same Km, changed Vmax). Uncompetitive: inhibitor binds only to enzyme-substrate complex. Both Km and Vmax decrease proportionally, so the ratio Vmax/Km stays constant — lines on a Lineweaver-Burk plot are parallel rather than intersecting, which is the diagnostic signature that distinguishes uncompetitive from the other inhibition types.

What should I know about Enzyme Inhibition in Medicine?

Many drugs work by enzyme inhibition. Statins: competitive inhibitors of HMG-CoA reductase (cholesterol synthesis). Penicillin: irreversible inhibitor of transpeptidase (bacterial cell wall synthesis). Aspirin: irreversible inhibitor of COX enzymes (prostaglandin synthesis). HIV protease inhibitors: competitive inhibitors preventing viral protein processing. Organophosphate pesticides and nerve agents: irreversible inhibitors of acetylcholinesterase (preventing nerve signal termination). Understanding exactly how a drug inhibits its target enzyme — competitively, non-competitively, or irreversibly — shapes both its dosing strategy (competitive inhibitors can be out-competed by excess substrate, so dose and timing matter more) and its safety profile, since irreversible inhibitors like nerve agents cause effects that persist until the body synthesises entirely new enzyme.