Enzyme Kinetics Calculator (Michaelis-Menten)

Enzyme Kinetics Guide

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 mean

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 alt

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

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). Underst