Download Irreversible Inhibition

20.5 Enzyme Inhibition
The structure of a noncompetitive inhibitor does not resemble
the substrate and does not compete for the active site.
Learning Goal Describe competitive and noncompetitive inhibition
and reversible and irreversible inhibition.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Inhibitors
Inhibitors
• are molecules that cause a loss of catalytic activity.
• prevent substrates from fitting into the active sites.
• can be classified as either reversible inhibitors or
irreversible inhibitors.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Reversible Inhibition
Reversible inhibitors
• cause a loss of enzyme activity that can be restored.
• can act in different ways but do not form covalent bonds
with the enzyme.
Reversible inhibition can be competitive or
noncompetitive.
• Competitive inhibitors compete for the active site.
• Noncompetitive inhibitors act on another site that is
not the active site.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Competitive Inhibitors
A competitive inhibitor
• has a chemical structure and polarity similar to the substrate.
• competes with the substrate for the active site.
• has its effect reversed by increasing substrate concentration.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Antimetabolites: Competitive Inhibitors in
Medicine
• Some bacterial infections are
treated with competitive inhibitors
called antimetabolites.
• Sulfanilamide competes with
p-aminobenzoic acid (PABA), an
essential metabolite in the growth
cycle of bacteria.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Noncompetitive Inhibitors
A noncompetitive inhibitor
• has a structure that is much different from that of the substrate.
• does not compete for the active site.
• distorts the shape of the enzyme, which prevents the binding of
the substrate at the active site.
• cannot have its effect reversed by adding more substrate.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Irreversible Inhibition
In irreversible inhibition, enzyme activity is destroyed when
• the inhibitor covalently bonds with R groups of an amino
acid that may be near the active site.
• the inhibitor changes the shape of the enzyme, which
prevents the substrate from entering the active site.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Irreversible Enzyme Inhibitors
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Enzyme Inhibition Summary
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Identify each description of an inhibitor that is either competitive
or noncompetitive.
A. Increasing substrate reverses inhibition.
B. It binds to the enzyme’s surface
but not to the active site.
C. Its structure is similar to that of
the substrate.
D. Inhibition is not reversed by adding
more substrate.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Identify each description of an inhibitor that is either competitive
or noncompetitive.
A. Increasing substrate reverses inhibition.
B. It binds to the enzyme’s surface
but not to the active site.
C. Its structure is similar to that of
the substrate.
D. Inhibition is not reversed by adding
more substrate.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
competitive
noncompetitive
competitive
noncompetitive
© 2016 Pearson Education, Inc.