Reversible Inhibition

Memory Hack💡

The prefix "un" means the opposite of: Uncompetitive inhibition has the opposite effects of competitive inhibition, as both the Vmax and Km decrease! Additionally, it is helpful to remember that instead of binding to a free enzyme and blocking it like how competitive inhibition does, it does the opposite, and binds to a nonfree enzyme. 

The prefix "non" means not: Noncompetitive inhibition is "not" competitive. Instead of binding to the active site, the inhibitor binds to a completely different space.

Notes

Reversible inhibition: Molecules bind noncovalently, meaning it is reversible. 

1. Competitive Inhibition: Inhibitor looks like the substrate and competes for binding to the active site. 

If you have ever taken an ecology class, you might be familiar with the term "competition" to refer to when organisms have to compete against each other for the same resource. This is exactly the same thing with enzymes! 

This effect somes with some consequences:  

Kinetics effects→ 

1. Vmax is unchanged. This is because it is still forming product!

2. Km seems to increase. Km is not actually increasing. Instead, it seems as though it is because there is less substrate binding and actually being converted to products. This makes it seem like the affinity is low, but it is actually unchanged. 

Note: you can overcome this type of inhibition by flooding the enzymes with substrate. 

So these next two are pretty similar sounding… 

2. Uncompetitive Inhibition: The inhibitor binds to a pocket that shows up on the ES complex (so only when the substrate is bound) and prevents it from becoming a product. 

Kinetics effects→ 

1. Vmax decreases.  

2. Km decreases 

Both of these results are because the enzyme cannot form a product with this type of inhibition. 

If you need some more review, please follow this link: https://www.youtube.com/watch?v=O23i38B2EmA 

3. Noncompetitive inhibition: The inhibitor can bind to both the free enzyme and the ES complex, as it does NOT bind the active site. It has its own place where it binds and affects the binding affinity of the enzyme to the substrate. 

Kinetic effects→ 

1. Vmax decreases. This is because as long as the inhibitor is bound, it will not form product. 

2. Km stays the same

If you need some more review, please follow this link: https://www.youtube.com/watch?v=4xOsAuj0QZg   

The image above shows the Lineweaver-Burke graph changes for each type of inhibition. 

These all make sense when you match up the kinetic effects for each!