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Enzyme Regulation. Regulation of Enzyme Activity. Enzyme quantity – regulation of gene expression (Response time = minutes to hours) Transcription Translation Enzyme turnover Enzyme activity (rapid response time = fraction of seconds) Allosteric regulation Covalent modification

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Presentation Transcript
regulation of enzyme activity
Regulation of Enzyme Activity

Enzyme quantity – regulation of gene expression (Response time = minutes to hours)

  • Transcription
  • Translation
  • Enzyme turnover

Enzyme activity (rapid response time = fraction of seconds)

  • Allosteric regulation
  • Covalent modification
  • Association-disassociation’
  • Proteolytic cleavage of proenzyme
allosteric regulation
Allosteric Regulation
  • End products are often inhibitors
  • Allosteric modulators bind to site other than the active site
  • Allosteric enzymes usually have 4o structure
  • Vo vs [S] plots give sigmoidal curve for at least one substrate
  • Can remove allosteric site without effecting enzymatic action
regulation of enzyme activity biochemical regulation

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Regulation of Enzyme Activity(biochemical regulation)
  • 1st committed step of a biosynthetic pathway or enzymes at pathway branch points often regulated by feedback inhibition.
  • Efficient use of biosynthetic precursors and energy
phosphofructokinase pfk
Phosphofructokinase( PFK)

Fructose-6-P + ATP ----->Fructose-1,6-bisphosphate + ADP

  • PFK catalyzes 1st committed step in glycolysis (10 steps total)
  • (Glucose + 2ADP + 2 NAD+ + 2Pi  2pyruvate + 2ATP + 2NADH)
  • Phosphoenolpyruvate is an allosteric inhibitor of PFK
  • ADP is an allosteric activator of PFK
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Allosteric modulators bind to site other than the active site and allosteric enzymes have 4o structure

Fructose-6-P + ATP ----->Fructose-1,6-bisphosphate + ADP

ADP

Allosteric Activator (ADP) binds distal to active site

vo vs s plots give sigmoidal curve for at least one substrate
Vo vs [S] plots give sigmoidal curve for at least one substrate

Binding of allosteric inhibitor or activator does not effect Vmax, but does alter Km

Allosteric enzyme do not follow M-M kinetics

allosteric t to r transition

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ET-I ET ER ER-S

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Concerted model

Sequential model

Allosteric T to R transition

S

covalent modification
Covalent modification
  • Regulation by covalent modification is slower than allosteric regulation
  • Reversible
  • Require one enzyme for activation and one enzyme for inactivation
  • Covalent modification freezes enzyme T or R conformation
phosphorylation dephosphorylation
Phosphorylation /dephosphorylation
  • most common covalent modification
  • involve protein kinases/phosphatase
  • PDK inactivated by phosphorylation
  • Amino acids with –OH groups are targets for phosphorylation
  • Phosphates are bulky (-) charged groups which effect conformation
enzyme regulation by association disassociation
Enzyme Regulation by Association/Disassociation
  • Acetyl-CoA Carboxylase
  • acetyl-CoA + CO2 + ATP  malonyl-CoA + ADP + Pi
  • 1St committed step in fatty acid biosynthesis
  • In presence of citrate activated
  • In presence of fatty acyl-CoA inactivated

citrate

polymerized

unpolymerized

Fatty acyl-CoA

blood clotting
Blood Clotting
  • Clotting involves series of zymogen activations
  • Seven clotting factors are serine proteases involved in clotting cascade rxns

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