Structural Biochemistry/Enzyme/Noncompetitive Inhibitor

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E + I − (through a substrate) → ES + I → E + P

ES + I ⇌ ESI → NR (no reaction)

where E is enzyme, I is inhibitor, ES is enzyme-substrate complex, P is product. ESI is the molecule after the inhibitor is bound to the enzyme-substrate complex. ESI cannot form any products, so the later reaction is not allowed (or, no reaction).

Noncompetitive Inhibitor

Noncompetitive kinetics

Based on the Michaelis-Menten Model, KM, the concentration of the substrate when the velocity is the half of the maximum velocity (or half of the substrates at maximum velocity), remains same, but the maximum velocity is decreased.


The picture shows a double-reciprocal plot of V0 and [S]. The x-intercept is equal to -1/Km while the y-intercept is 1/Vmax. The slope of the line is Km/Vmax. Thus, the plot shows that there is no change in Km and Vmax is decreased. In relation to the original plot, the x intercept stays constant while the y intercept increases along with the slope.

File:Noncompetitive inhibitor.jpg


Berg, Jeremy M., John L. Tymoczko, and Lubert Stryer. BIOCHEMISTRY. 6th ed. New York: W. H. FREEMAN AND COMPANY, 2007.

Reece, Jane (2011). Biology. Pearson. ISBN 978-0-321-55823-7.