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Inhibitors
Sara_6571
#1 Posted : Tuesday, May 11, 2021 8:38:37 PM
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Could someone please explain to me the types of irreversible inhibition vs the reversible inhibition types?
Youssef_6546
#2 Posted : Wednesday, May 12, 2021 6:44:57 AM
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Hi Sara,

From what I know, reversible inhibition occurs when the inhibitor binds to the enzyme’s active site via a non-covalent interaction (i.e. H-bonds, hydrophobic bonds, and other intramolecular interactions). With non-covalent bonds, it is temporary, so the inhibitor could basically get knocked-off by a substrate or another inhibitor that more specifically binds to the active site (as seen in competitive inhibition, which is relieved by increasing # of substrates). As for irreversible inhibition, the inhibitor forms covalent bonds with the enzyme’s active site. Covalent bonds are intramolecular interactions (e.g. the bond between two chloride atoms to make Cl2, and the double bond between two oxygen atoms to make O2). These are stronger that non-covalent bonds, which explains why it is irreversible. As for examples, toxins are usually common irreversible inhibitors.

Hope these help!
INSTR_Sydney_132
#3 Posted : Thursday, May 20, 2021 4:43:16 PM
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Hi Sara (and thank you Youssef for your detailed answer!)

Indeed as Youssef mentioned, irreversible inhibition occurs when some covalent modification occurs on the enzyme, permanently eliminating it. This cannot be overcome by adding more substrate.

However, the most common type of enzymatic inhibition you will see on the MCAT (and a very high yield topic) is reversible inhibition. They are reversible because the inhibitor that binds to the enzyme will eventually come off. They temporarily deactivate the enzyme in contrast to irreversible ones that destroy the enzyme all together.

The 4 types of reversible inhibitors you will see on the MCAT are competitive, non-competitive, uncompetitive, and mixed inhibition.

In competitive inhibition: An inhibitor will bind to an enzyme and block binding of the substrate. This is called competitive inhibition, because the inhibitor “competes” with the substrate for the enzyme.

In noncompetitive inhibition, the inhibitor doesn't block the substrate from binding to the active site. Instead, it attaches at another site and blocks the enzyme from doing its job.

In uncompetitive inhibition, the inhibitor binds selectively to the enzyme-substrate (ES) complex.

Mixed inhibition is a type of enzyme inhibition in which the inhibitor may bind to the enzyme OR the enzyme substrate complex, but typically has a greater affinity for one or the other.

Hope this helps! - Sydney
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