40
µmol/min
66.6667
µmol/min
15
mM
3
x
60
%
40
%
40
µmol/min
66.6667
µmol/min
15
mM
3
x
60
%
40
%
The Competitive Inhibition Ki calculator models enzyme kinetics in the presence of a competitive inhibitor. Competitive inhibitors bind to the enzyme's active site, competing directly with the substrate for access. This increases the apparent Km while leaving Vmax unchanged, since high substrate concentrations can outcompete the inhibitor.
Understanding competitive inhibition is crucial in pharmacology where many drugs act as competitive inhibitors, and in metabolic regulation where pathway intermediates may inhibit competing enzymes. This calculator shows the inhibited velocity, the degree of inhibition, and how the apparent Km shifts.
In competitive inhibition, the velocity equation becomes:
v = Vmax × [S] / (Km × (1 + [I]/Ki) + [S])
The apparent Km increases by the factor (1 + [I]/Ki):
Km(apparent) = Km × (1 + [I] / Ki)
The inhibition percentage compares the inhibited velocity to the uninhibited velocity. A lower Ki indicates a more potent inhibitor that reduces velocity more effectively at a given concentration.
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With [I]/Ki = 2, the apparent Km triples from 5 to 15 mM. The velocity drops from 66.7 to 40 µmol/min, a 40% reduction at this substrate concentration.
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At high substrate (100 mM >> Km), the inhibitor's effect is largely overcome. Only 8.7% inhibition remains because substrate outcompetes the inhibitor for the active site.
In competitive inhibition, the inhibitor competes with substrate for the active site, increasing apparent Km but not affecting Vmax. In uncompetitive inhibition, the inhibitor binds only the enzyme-substrate complex, decreasing both Vmax and Km. In mixed (non-competitive) inhibition, both Vmax and Km are affected.
A low Ki indicates a potent inhibitor that binds tightly to the enzyme active site. Less inhibitor is needed to achieve significant enzyme inhibition. Most effective pharmaceutical competitive inhibitors have Ki values in the nanomolar to micromolar range.
Yes, competitive inhibition can theoretically be fully overcome by increasing substrate concentration to levels that vastly exceed the apparent Km. At sufficiently high [S], the enzyme reaches its uninhibited Vmax because substrate outcompetes the inhibitor for active site binding.
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