Enzymes

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Enzymes
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Enzymes

• Enzyme- highly specific protein catalysts

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Enzyme Specificity
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Enzyme Specificity

• Lock and Key model
• Induced fit model
• polyaffinity mechanism- three point attachment

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Catalyst

• Catalyst- speeds up reaction without being
  consumed (no effect on equilibrium)
• do so by lowering the activation energy of the
  rxn
• activation energy- the amount of energy required
  to reach the transition state

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Catalyst

• Catalyst- speeds up reaction without being
  consumed
• do so by lowering the activation energy of the
  rxn
• activation energy- the amount of energy required
  to reach the transition state

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Classes of Enzymes

• Enzyme Commission (E.C.) 4.1.1.32
• 1. Oxidoreductases

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Coenzymes

• Coenzyme- organic molecule required by an enzyme
  to catalyze rxn
• Most coenzymes are vitamin derivatives (water sol)

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Classes of Enzymes

• Enzyme Commission (E.C.) 4.1.1.32
• 1. Oxidoreductases- lactate dehydrogenase
• 2. Transferases- glucokinase
• 3. Hydrolases- chymotrypsin, G6Pase
• 4. Lyases- fumarase
• 5. Isomerases- phosphoglucoisomerase
• 6. Ligases- Acyl CoA synthetase

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Classes of Enzymes

• 1. Oxidoreductases
• 2. Transferases
• 3. Hydrolases
• 4. Lyases
• 5. Isomerases
• 6. Ligases

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Cofactors and Coenzymes

• Cofactor- depends on context
• either inorganic atom
• or inorganic molecule or coenzyme
• Coenzyme- organic molecule required by an enzyme
  for its catalytic activity, usually vitamin or
  vitamin derivative

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Coenzymes

• 1. Oxidoreductases
• NAD/NADH H
• NADP/NADPH H
• FAD/FADH2

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NAD/NADH

• Niacin derivative
• recognize structure
• used for degradation
• diffuses in and out of active site

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NADP/NADPH

• Almost identical to NAD
• used for synthesis
• diffuses in and out of active site

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FAD/FADH2

• Riboflavin derivative
• used for degradation
• Prosthetic group

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Coenzymes (table of vitamin, coenz form and
function)

• 2. Transferases
• TPP
• THF
• PLP
• lipoic acid
• vitamin B12
• CoASH
• 6. Ligases
• biotin

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Kinetics Rate of Reaction
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Kinetics Rate of Reaction
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Kinetics Rate of Reaction
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Kinetics Rate of Reaction
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Michaelis-Menton Kinetics

• Eqn.
• Vo
• Vmax
• Km
• S

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Lineweaver-Burk Transformation

• Eqn of transformation
• slope and intercepts

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Michaelis-Menton Kinetics Substrate Concentration
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Michaelis-Menton Kinetics Enzyme concentration
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Michaelis-Menton KineticsTemperature
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Michaelis-Menton KineticspH
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Michaelis-Menton Kinetics Inhibitors or activators

• Activators- not discussed at this time
• Inhibitors- 3 types

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Enzyme Inhibition

• Competitive inhibition-
• Noncompetitive inhibition-
• Uncompetitive inhibition-

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Example Problem

• S,µmol vo, µmol/min
• 0.1 0.27
• 2.0 5
• 10.0 20
• 20.0 40
• 40.0 64
• 60.0 80
• 100.0 100
• 200.0 120
• 1000.0 150
• 2000.0 155

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Michaelis-Menton Plot
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Example Problem

• S,µmol 1/S, µmol-1 vo, µmol/min
  1/vo, min/µmol
• 0.1 10 0.27 3.70
• 2.0 0.5 5 0.2
• 10.0 0.1 20 0.05
• 20.0 0.05 40 0.025
• 40.0 0.025 64 0.0156
• 60.0 0.0167 80 0.0125
• 100.0 0.01 100 0.01
• 200.0 0.005 120 0.0083
• 1000.0 0.001 150 0.0067
• 2000.0 0.0005 155 0.0065

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Lineweaver-Burk Plot
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Type of Inhibition
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Enzyme Active Sites

• Active site- that region of the enzyme where
  substrate binds and is converted to product
• why the enzyme has to be bigger than substrate

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Ways in Which an Enzyme Performs Catalysis

• Increase the effective concentration
• Stabilize transition state
• Put a strain on susceptible bonds
• Hold reactants near each other and in the proper
  orientation
• Form covalent bonds with substrate that result in
  destabilization of substrate
• Act as proton donors and acceptors
• Nucleophilic/Electrophilic attacks

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Amino Acids of the Active Siteget good example
of each

• X-ray crystallography
• mutagenesis
• amino acid modifying reagents

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Enzyme Regulation

• On vs. off
• 1. Isoenzymes 2. Covalent
  Modification 3. Allosterism 4.
  Repression 5. Proenzymes

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Isoenzymes

• LDH example
• muscle vs. heart
• tetramer
• preferential substrate affinity
• why?

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Covalent Modification

• Phosphorylation most common
• Others sulfation, acetylation, methylation
• glycogen phosphorylase vs. glycogen synthase

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Allosteric Activation/Inhibition

• Other site
• Sigmoidal kinetics
• homo- vs. heterotropic
• feedback inhibition vs. feedforward stimulation

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Repression

• molecular biology section

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Proenzymes

• AKA zymogens
• alters the concentration of active enzyme
• particularly common with digestive
  enzymes peptide hormones clotting factors
• proteolysis is selective
• dibasic example

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Proinsulin
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Other Cleavages