Noncompetitive and Uncompetitive Inhibition
Noncompetitive Inhibition:
In this case the inhibitor binds to both E and ES. Both the slope (KM/Vmax), and the Y-intercept (1/Vmax) of the Lineweaver-Burk plot increase The KI ('s) are determined as above by replotting the slope and intercept values vs. [I].
1. Vmax is decreased: At high levels of substrate the inhibitor is still bound.
2. KM is increased: Higher [S] is required to reach the lower maximal velocity. (For "simple noncompetitive inhibition", KM is not changed)
Uncompetitive Inhibition
1. The inhibitor binds directly to the ES complex.
2. The inhibitor does not have to bind at the active site.
3. The inhibitor does not have to resemble the substrate (e.g. an allosteric inhibitor).
Vmax is reduced: the amount of ESI formed depends on [I]. The solution to the steady-state equation results in the (1 + [I]/KI) factor multiplying the [S] term in the denominator of the Michaelis-Menten equation.
The slopes of the Lineweaver-Burk plot (KM/Vmax) are unchanged, but the Y-intercept increases by a factor of (1 + [I]/KI). The X-intercept shifts to the left by a factor (1 + [I]/KI).
