Biochemistry 304: Mixed Inhibition

[liveonearth]

-Km, Vmax, and Kcat are affected
-directly affect Kcat
-metal ions often act as noncompetitive enzyme inhibitors, ex: trivalent ions like Al3+ inhibits acetylcholinesterase.
-binds somewhere other than active site causing a change in enzyme conformation that affects the structure or chemical properties of the active site
-lowers Vmax and usually increases Km but can rarely lower it
-noncompetitive inhibitor
-you can't overcome the effect by adding more substrate
-when the inhibitor affects only Kcat and not Km, the inhibition is said to be noncompetitive, does not prevent (or even influence?) substrate binding to the active site

Acetylcholine (the neurotransmitter) is hydrolyzed by the enzyme acetylcholinesterase to form acetate and choline. Inhibit this enzyme and you can get tetanus. Some bacterial toxins can inhibit it. Botchilinum causes acetylcholine to be broken down too fast, and causes "flaccid paralysis". Aluminum 3+ inhibits acetylcholine by binding on the side of the free enzymes or ES comples. This is an example of allosteric inhibition.