Biochemistry : Uncompetitive Inhibition
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Example Question #1 : Uncompetitive Inhibition
An uncompetitive inhibitor binds to which of the following?
The active site of the enzyme before the substrate has a chance to bind
An allosteric site on the enzyme only when the substrate has not yet bound to the active site
The active site of the enzyme at the same time as the substrate
An allosteric site on the enzyme, regardless of whether or not the substrate is already bound to the active site
An allosteric site on the enzyme, only when the substrate is already bound to the active site
An allosteric site on the enzyme, only when the substrate is already bound to the active site
Uncompetitive inhibition occurs when an inhibitor binds to an allosteric site of a enzyme, but only when the substrate is already bound to the active site. In other words, an uncompetitive inhibitor can only bind to the enzyme-substrate complex.
Example Question #2 : Uncompetitive Inhibition
Which of the following changes occurs when an uncompetitive inhibitor binds to the enzyme-substrate complex?
Uncompetitive inhibition occurs when an inhibitor binds to an allosteric site on the enzyme, but only when it is an enzyme-substrate complex. Because the inhibitor binds to the enzyme-substrate complex and then changes the enzyme's conformation, it makes it incredibly difficult for the substrate to become unbound from the enzyme. Thus, the apparent affinity of the substrate for the enzyme is dramatically increased. A decrease in 
Example Question #3 : Uncompetitive Inhibition
Which of the following is true about noncompetitive inhibition?
The inhibitor binds to the same site as the substrate, dropping the Km
The inhibitor competes with the substrate to bind to the active site, and drops the Vmax
The inhibitor binds independently of substrate binding however km does not change
Vmax stays the same, however Km increases
The inhibitor binds to a separate site from the substrate and enhances enzyme activity
The inhibitor binds independently of substrate binding however km does not change
With uncompetitive inhibitors, the inhibitor binds to a site separate from the binding site of the substrate. This can occur even while the substrate is bound to the enzyme, blocking the process and reduce the catalysis of the enzyme.
This will result in the reduction of Vmax because the enzymes ability for catalysis is being reduced by the binding of inhibitor to the enzyme-substrate complex. Km does not change because the substrate and the uncompetitive inhibitor bind to different sites.
Example Question #4 : Uncompetitive Inhibition
Which of the following is true of uncompetitive inhibitors of enzymes?
They lower the concentration of free enzyme available to bind to substrate.
There effect can be countered by adding more substrate.
They bind to both the enzyme-substrate complex and the free enzyme.
They decrease the apparent KM and increase the apparent VM on a Lineweaver-Burke plot.
They only affect enzymes that act on multiple substrates.
They only affect enzymes that act on multiple substrates.
The correct answer is that uncompetitive inhibitors of enzymes only affect enzymes that act on multiple substrates. Uncompetitive inhibitors bind to the enzyme-substrate complex only, not to the free enzyme. They distort the active site to prevent the enzyme from being catalytically active without actually blocking the binding of the substrate. This cannot occur with an enzyme that only acts on a single substrate at a time. Adding more substrate and lowering the amount of free enzyme available both apply to competitive inhibitors, which bind to free enzymes and block the substrate-binding site of the enzyme. Uncompetitive inhibitors do decrease the apparent KM on a Lineweaver-Burke plot, but they also lower the apparent VM.
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