Uncompetitive inhibition

Uncompetitive inhibition (which Laidler and Bunting preferred to call anti-competitive inhibition, but this term has not been widely adopted) is a type of inhibition in which the apparent values of the Michaelis–Menten parameters ${\displaystyle V}$ and ${\displaystyle K_{\mathrm {m} }}$ are decreased in the same proportion.

It can be recognized by two observations: first, it cannot be reversed by increasing the substrate concentration ${\displaystyle a}$, and second, linear plots show effects on ${\displaystyle V}$ and ${\displaystyle K_{\mathrm {m} }}$, seen, for example, in the Lineweaver–Burk plot as parallel rather than intersecting lines. It is sometimes explained by supposing that the inhibitor can bind to the enzyme-substrate complex but not to the free enzyme. This type of mechanism is rather rare, and in practice uncompetitive inhibition is mainly encountered as a limiting case of inhibition in two-substrate reactions in which one substrate concentration is varied and the other is held constant at a saturating level.