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BCH 415
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edu
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220- 228)
Many enzyme activities are regulated in response to environmental changes in the cell (glucose or amino acid
levels etc
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Often, these regulatory enzymes are found early in a complicated
pathway so that energy isn’t wasted
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Allosteric control
2
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Protein processing
1
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Involves the binding of small molecules (modulators) to the enzyme that affect the substrate binding ability
through a conformation change in the enzyme
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e
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These enzymes
tend to be complicated and have multiple subunits
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Heterotropic: regulatory enzymes where the modulator is something other than the substrate
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However, ATP enhances the affinity of ATCase for its substrates
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This indicates cooperative binding of
substrates
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5 (the
substrate concentration for half-maximal velocity)
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2
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Modifying groups are (pp
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Adenylylation: adenylyl group added
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ADP-ribosylation: adenosine diphosphate ribosyl group added (e
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diphtheria toxin)
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Phosphorylation is a major modification of enzymes in cells:
Phosphoryl is attached by a protein kinase and removed by a protein phosphatase
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Glycogen phosphorylase: This enzyme removes glucose from glycogen which is stored in the muscle and liver
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Glycogen phosphorylase activity is regulated by phosphorylation at Ser14
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The phosphorylation event is controlled by a
hormone cascade that starts with epinephrine (adrenaline)
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BCH 415
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edu
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Glycogen synthase uses a
complicated series of phosphorylation events to alter its activity (pp
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This enzyme is important to build
glycogen stores and this process needs to be carefully regulated
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Protein processing
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Common in
proteolytic enzymes since these enzymes need to be made in an inactive form, then activated when they are
needed in the correct place (e
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stomach)
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It becomes active in the small
intestine where it is cleaved into trypsin by the enzyme enteropeptidase (secreted by the intestinal gland
cells)
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These enzymes can only be inactivated by other inactivating proteins binding to them like trypsin inhibitor
for trypsin

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