Download Digestive Enzymes

Chapter 20 Enzymes and Vitamins
20.5
Control of Enzyme Activity
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
1
Zymogens
Zymogens (proenzymes)
 Are inactive forms of
enzymes.
 Are activated when
one or more peptides
are removed.
 Such as proinsulin is
converted to insulin by
removing a small
Copyright © 2007 by Pearson Education, Inc.
peptide chain.
Publishing as Benjamin Cummings
2
Digestive Enzymes
Digestive enzymes are
 Produced as zymogens in one organ and transported
to another such as the pancreas when needed.
 Activated by removing small peptide sections.
TABLE 20.7
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
3
Digestive Enzymes
Zymogen
(from pancreas)
Active Enzyme
(in small intestine)
enteropeptidase
trypsinogen
trypsin + peptide
trypsin
chymotrypsinogen
chymotrypsin + 2 dipeptides
trypsin
procarboxypeptidase
carboxypeptidase + peptide
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Allosteric Enzymes
An allosteric enzyme is
 An enzyme in a reaction sequence that binds a
regulator substance.
 A positive regulator when it enhances the
binding of substrate and accelerates the rate of
reaction.
 A negative regulator when it prevents the binding
of the substrate to the active site and slows
down the rate of reaction.
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Feedback Control
In feedback control
 A product acts as a negative regulator.
 An end product binds with the first enzyme (E1) in
a sequence when sufficient product is present.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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Learning Check
Identify each statement as:
zymogen (Z)
allosteric enzyme (A)
positive regulator (PR)
feedback control (FC)
1. An enzyme in a pathway that controls the rate of the
reaction.
2. Speeds up a reaction by combining with an
enzyme in the pathway.
3. Removal of a peptide activates the enzyme.
4. Some product binds to the first enzyme to limit the
synthesis of product.
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Solution
Identify each statement as:
zymogen (Z)
allosteric enzyme (A)
positive regulator (PR)
feedback control (FC)
1. A
An enzyme in a pathway that controls the rate of
the reaction.
2. PR Speeds up a reaction by combining with an
enzyme in the pathway.
3. Z Removal of a peptide activates the enzyme.
4. FC Some product binds to the first enzyme to limit the
synthesis of product.
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