ch06 enzyme 2
TRANSCRIPT
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Concepts in Biochemistry
Third Edition
Chapter 6:
Enzymes II: Cofactors, Regulation, andCatalytic RNA
Copyright 2006 by John Wiley & Sons, Inc.
Rodney Boyer
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Cholineessential
nutrient
Rapid brain
development, enhance
memory and slows
progression of
Alzheimers disease;improves liver and
cardiovascular
function
Rich sources: fish,
eggs, soybeans, liver,cauliflower, peanuts
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Enzyme and coenzymes
Some enzymesbiologically active in their
native state
Some require cofactors for activity
Holoenzyme = apoenzyme (protein) +
cofactor
Cofactors: metal ions; small organic molecule
called coenzymesvitamin derivatives
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Enzyme regulation
Enzyme activities in metabolic pathwaysare subject to regulation
Allosteric enzymesregulatory enzymes;- Influenced by noncovalent binding of signal
molecules (positive effectors or negative
effectors)- Oligomeric (several subunits)
- Have both catalytic and regulatory sites
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Homotropic allosterism
Substrate and effector are the same type of
molecule
Several catalytic sites; identical subunits
The binding of one substrate to a catalytic
site influences the binding of other
substrates to the catalytic site (positivecooperativity)
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Sigmoidal
curve
characteristic
of positivecooperativity
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Heterotropic allosterism
Effector molecule is different from the
substrate
regulatory subunit and catalytic subunit aredifferent
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MWC concerted model of positive
cooperativity
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Sequential model ofpositive
cooperativity by
Koshland
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Other forms of enzyme regulation
Covalent modification of enzymes
chemical alteration of the enzyme
- phosphorylation/dephosphorylation of OHgrps of serine, threonine or tyrosine
- adenylylation
- Reduction of disulfide bonds
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Activation by proteolytic cleavage of a
proenzyme
Zymogensinactive precursor of enzymes
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Regulation by different molecular forms -
isoenzymes
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