chemistry 2100 lecture 11. protein functions + pl p l binding catalysis structure
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Chemistry 2100
Lecture 11
Protein Functions
+
PLPL
Binding
Catalysis
Structure
Why Enzymes?• Higher reaction rates• Greater reaction specificity• Milder reaction conditions• Capacity for regulation
COO
OH
O COO
COO
O COO
NH2
OOCCOO
O
OH
OH
COO
NH2
COO
-
-
-
-
-
-
--
Chorismate mutase
• Metabolites have many potential pathways of decomposition
• Enzymes make the desired one most favorable
Specificity: Lock-and-Key Model
• Proteins typically have high specificity: only certain substrates bind
• High specificity can be explained by the complementary of the binding site and the ligand.
•Complementarity in
– size,
– shape,
– charge,
– or hydrophobic / hydrophilic character
•“Lock and Key” model by Emil Fisher (1894) assumes that complementary surfaces are preformed.
+
Specificity: Induced Fit
• Conformational changes may occur upon ligand binding (Daniel Koshland in 1958). – This adaptation is called the induced fit. – Induced fit allows for tighter binding of the
ligand– Induced fit can increase the affinity of the
protein for a second ligand
• Both the ligand and the protein can change their conformations
+
Apoenzyme + Coenzyme = Holoenzyme
Apoenzyme + Coenzyme = Holoenzyme
Apoenzyme + Coenzyme = Holoenzyme
Apoenzyme + Coenzyme = Holoenzyme
• increase [reactant]
• increase temperature
• add catalyst
Pote
nti
al Energ
y
Reaction
Reactants
Products
Enzymatic Activity
• increase [reactant]
• increase temperature
• add catalyst
Pote
nti
al Energ
y
Reaction
Reactants
Products
TS
• increase [reactant]
• increase temperature
• add catalyst
Pote
nti
al Energ
y
Reaction
Reactants
Products
Ea
TS
• increase [reactant]
• increase temperature
• add catalyst
Pote
nti
al Energ
y
Reaction
TS
Reactants
Products
Ea
• increase [reactant]
• increase temperature
• add catalyst
Pote
nti
al Energ
y
Reaction
Reactants
Products
Ea
TS
• increase [reactant]
• increase temperature
• add catalyst
Pote
nti
al Energ
y
Reaction
Reactants
Products
Ea
TS
Ea'
• increase [reactant]
• increase temperature
• add catalyst
Reactants
Products
Pote
nti
al Energ
y
Reaction
Ea
TS
How to Lower G?Enzymes organizes reactive groups into
proximity
How to Lower G?Enzymes bind transition states best
Pote
nti
al Energ
y
Reaction
O C OH2O +
HO C O– + H+
O
H2O + CO2 HOCO2– + H+
Pote
nti
al Energ
y
Reaction
H2O + CO2 HOCO2– + H+
H2O + O C O
Pote
nti
al Energ
y
Reaction
H2O + CO2 HOCO2– + H+
H2O + O C O
HO C O– + H+
O
Pote
nti
al Energ
y
Reaction
H2O + CO2 HOCO2– + H+
H2O + O C O
HO C O– + H+
O
Pote
nti
al Energ
y
Reaction
H2O + CO2 HOCO2– + H+
O C O
O
H
H
H2O + O C O
HO C O– + H+
O
Pote
nti
al Energ
y
Reaction
H2O + CO2 HOCO2– + H+
O C O
O
H
H
H2O + O C O
HO C O– + H+
O
Ea
H2O + CO2 HOCO2– + H+
Pote
nti
al Energ
y
Reaction
Ea
Ea'
O C O
O
H
H
H2O + O C O
HO C O– + H+
O
[ sucrose-sucrase complex ] H2O
sucrase
sucrose glucose
fructose
sucrase
++
+
[ sucrose-sucrase complex ] H2O
sucrase
sucrose glucose
fructose
sucrase
++
+
[ sucrose-sucrase complex ] H2O
sucrase
sucrose glucose
fructose
sucrase
++
+
[ sucrose-sucrase complex ] H2O
sucrase
sucrose glucose
fructose
sucrase
++
+
[ sucrose-sucrase complex ] H2O
sucrase
sucrose glucose
fructose
sucrase
++
+
[ sucrose-sucrase complex ] H2O
sucrase
sucrose glucose
fructose
sucrase
++
+
[ sucrose-sucrase complex ] H2O
sucrase
sucrose glucose
fructose
sucrase
++
+
[ sucrose-sucrase complex ] H2O
sucrase
sucrose glucose
fructose
sucrase
++
+
How to Do Kinetic Measurements
Enzyme ActivityFigure 23.3 The effect of enzyme concentration on the rate of an enzyme-catalyzed reaction. Substrate concentration, temperature, and pH are constant.
Enzyme ActivityFigure 23.4 The effect of substrate concentration on the rate of an enzyme-catalyzed reaction. Enzyme concentration, temperature, and pH are constant.
Enzyme ActivityFigure 23.5 The effect of temperature on the rate of an enzyme-catalyzed reaction. Substrate and enzyme concentrations and pH are constant.
Enzyme ActivityFigure 23.6 The effect of pH on the rate of an enzyme-catalyzed reaction. Substrate and enzyme concentrations and temperature are constant.
What equation models this behavior?
Michaelis-Menten Equation
H2 O
acetic acidcholine (Ch)
acetylcholine (ACh)
OHCH2(CH3 )3 N CH2
CH3CCH2(CH3 )3 N CH2 O
O
CH3CHO
O
+
+
AChE
H2 O
acetic acidcholine (Ch)
acetylcholine (ACh)
OHCH2(CH3 )3 N CH2
CH3CCH2(CH3 )3 N CH2 O
O
CH3CHO
O
+
+
AChE
H2 O
acetic acidcholine (Ch)
acetylcholine (ACh)
OHCH2(CH3 )3 N CH2
CH3CCH2(CH3 )3 N CH2 O
O
CH3CHO
O
+
+
AChE
H2 O
acetic acidcholine (Ch)
acetylcholine (ACh)
OHCH2(CH3 )3 N CH2
CH3CCH2(CH3 )3 N CH2 O
O
CH3CHO
O
+
+
AChE
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H O
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H O
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H O
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H O
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H O
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H O
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H O
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H O
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
Asp
COOH
His
Ser
NHN
HO
CH2
COO
H
CH3
OCH2(CH3)3N CH2 C O
Glu
••
H
H2 O
acetic acidcholine (Ch)
acetylcholine (ACh)
OHCH2(CH3 )3 N CH2
CH3CCH2(CH3 )3 N CH2 O
O
CH3CHO
O
+
+
AChE
Inhibitors
• Reversible inhibitors– Temporarily bind enzyme and prevent
activity
• Irreversible inhibitors– Permanently bind or degrade enzyme
Reversible Inhibition
Irreversible Inhibition
••
Glu
COOH
O
CH2
NHN
Ser
His
COOH
Asp
Acetylcholinesterase
••
Glu
COOH
O
CH2
NHN
Ser
His
COOH
Asp
OP
CH3
OCH
CH3
CH3
F
••
Glu
COOH
O
CH2
NHN
Ser
His
COOH
Asp
OP
CH3
OCH
CH3
CH3
F
••
Glu
COOH
O
CH2
NHN
Ser
His
COOH
Asp
OP
CH3
OCH
CH3
CH3
F
••
Glu
COOH
O
CH2
NHN
Ser
His
COOH
Asp
OP
CH3
OCH
CH3
CH3
F
••
Glu
COOH
O
CH2
NHN
Ser
His
COOH
Asp
OP
CH3
OCH
CH3
CH3
F
BrBr
succinylcholine
decamethonium bromide
(CH3 )3 N–CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2–N(CH 3 )3
CH2CH2OCCH2CH2COCH2CH2 N(CH 3 )3(CH3 )3 N
O O
Pyridine aldoxime methiodide (PAM)
IN
CH3
CH N OH
• lactase
• rennin
• papain
• high-fructose corn syrup
• pectinase
• clinical assays
Commercial Enzymes
• lactase
• rennin
• papain
• high-fructose corn syrup
• pectinase
• clinical assays
• lactase
• rennin
• papain
• high-fructose corn syrup
• pectinase
• clinical assays
• lactase
• rennin
• papain
• high-fructose corn syrup
• pectinase
• clinical assays
starch dextrins glucose fructose α-amylase glucoamylase glucose
isomerase
starch dextrins glucose fructose α-amylase glucoamylase glucose
isomerase
starch dextrins glucose fructose α-amylase glucoamylase glucose
isomerase
• lactase
• rennin
• papain
• high-fructose corn syrup
• pectinase
• clinical assays
• lactase
• rennin
• papain
• high-fructose corn syrup
• pectinase
• clinical assays
• lactase
• rennin
• papain
• high-fructose corn syrup
• pectinase
• clinical assays
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