Inhibition

[RH8448]

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Before I get into this biochem question I just want to note that I am finding a lot of false information on the types of inhibitors and what they do. Errors can go wrong conceptually and graphically. I've seen videos and other websites either not describe very well or were wrong.

I want to compare Mixed with Uncompetitive and while I'm at it non competitive.

Mixed will raise the Km and lower the Vmax. In other words the inhibitor lowers the affinity of the enzyme substrate interaction and binds to the ES complex to lower kcat making the product formation lower.

Now, Uncompetitive inhibitors attach only to the ES complex allosterically clearly lowering the product formation. However, the Km happens to decrease. Why would Km decrease?, this means that the enzyme is able to bind more substrates. Is it because when the ES complexes are bound an equilibrium shift occurs?

In NonCompet, the inhibitor binds to E and ES and only affects the Vmax - has nothing to do with Km

 

[NeuroMaster316]

Why would Km decrease?

Think of it in terms of a chemical reaction. The uncompetitive inhibitor will bind the ES complex, i.e. it's disappearing (the product yield decreases), so to compensate the equilibrium will shift to the left to form more ES complexes which also increases inhibition, i.e. more substrate will bind to the free enzymes giving the APPEARANCE of decreased Km just as the Km APPEARS to increase in competitive inhibition. Remember the Km is constant for an enzyme.