Enzyme Inhibition Calculator

Calculate enzyme inhibition constant Ki, IC50, and type of inhibition from kinetic data.

Inhibition type

Km uninhibited (mM) (mM)

Km apparent with inhibitor (mM) (mM)

For competitive: Km increases

Inhibitor concentration [I] (mM) (mM)

Vmax uninhibited (μmol/min)

Vmax apparent with inhibitor (μmol/min)

For non-competitive: Vmax decreases

Please check your inputs and try again.

Worked Examples

Example 1: Competitive: Km=2→5mM, [I]=1mM

α=5/2=2.5, Ki=1/(2.5-1)

Result: Ki = 0.67 mM

Moderate competitive inhibitor

Example 2: Non-competitive: Vmax=100→50, [I]=2mM

α=100/50=2, Ki=2/(2-1)

Result: Ki = 2 mM

Non-competitive at [I]=Ki

Frequently Asked Questions

Competitive vs non-competitive inhibition?

Competitive: inhibitor resembles substrate, binds active site. Overcome by high [S]. Km increases, Vmax unchanged. Non-competitive: binds allosteric site. Cannot overcome with substrate. Vmax decreases, Km unchanged.

What is IC50 vs Ki?

IC50 is concentration causing 50% inhibition — depends on assay conditions. Ki is the true dissociation constant of inhibitor from enzyme — independent of assay conditions. Ki is preferred for comparing inhibitors.