Alcohol metabolism – the role of K M
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Transcript of Alcohol metabolism – the role of K M
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Alcohol metabolism – the role of KM
Cytosolic AcetaldehydedehydrogenaseKM value - high
Mitochondrial Acetaldehyde
reductaseKM value - low
CH3 CH2 OH NAD+
CH3 CHO
H+
NADHCH3 CHO
NAD+ H+
NADHCH3 COOH
+ + +
Alkoholdehidrogenáz
+ + +
Acetaldehiddehidrogenáz
TACHYCARDIA
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Enzymes - KM values
Enzyme Substrate KM
Chymotrypsin Acetil-L-Trp 5000 mM
ß-Galaktosidase Lactose 4000 mM
Penicillinase Benzylpenicillin 50 mM
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KM
1
32M k
kkK
E + S E + PES
k1
k2
k3
32 kk 1
2M k
kK
1
2ES k
k
[ES]
[S]*[E]K
KM ~ Dissociation constant for ES, if k2 >> k3
KM value is high: ES formation is weakKM value is low : assotiation
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Importance of the Vmax value
Turnover number:
t3max [E]kV tmax3 /[E]Vk
Enzyme Turnover number / sec
Carbonic anhydrase 600000
Acetylcholin esterase 25000
Tryptophan synthetase 2
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Inhibition of Enzymes
• Irreversible– Ser-OH– Cys-SH
• Reversible
CH2 OH
C
H
CH3H3C
O
P
O
OF
C CH3H3C
H
+
C
H
CH3H3C
O
P
O
O
C CH3H3C
H
OCH2Enzim Enzim
Diizopropil-fluorofoszfát
+ HFEnzyme Enzyme
Diisopropylfluorophosphate
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Inhibitions of enzymes
Enzim EnzimCH2 SH ICH2 C NH2
O
+ CH2 S CH2 C NH2
O
HFMonojód acetamid
•-SH enzymes
+ HIEnzyme Enzyme
monoiodacetamide
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Competitive inhibition of succinate-dehydrogenase by malonate
COO-
CH2
CH2
COO-
COO-
CH
CH
COO-
COO-
CH2
COO-
COO-
COO-
COO-
CH2
C
COO-
O
PO O
O
O
P
O
OO
FAD FADH2
Succinate-dehydrogenase
malonate
Oxalate
Oxaloacetate
pyrophosphate
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Competitive inhibition
+ S
+ I
E + S ES E + P
I
EI
Ki
+
EI
I*EK i
Ki = dissociation constant for complex
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Competitive inhibition of succinate-dehydrogenase by malonate
[Inhibitor 1]
[Enzyme]
[Inhibitor 2]
No inhibitor
Substrate+ competitive inhibitor
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Competitive inhibition
+ S
+ I
E + S ES E + P
I
EI
Ki
+
EI
I*EK i
Ki = Dissociation constans of complex
+P
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Competitive inhibition of succinate-dehydrogenase by malonate
Substrate [M]
Enzyme without ihhibitor
V [M/min]
Enzyme + inhibitor (1)
Enzyme + inhibitor (2)
Vmax
Vmax/2
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Competitive inhibition
1/[S]
1/v
y=a*x+b
MaxMax
m
V
1
S
1*
V
K
v
1
MaxiMax
m
V
1
S
1*)]
K
I(1
V
K
v
1[
1/VMAX
Enzyme alone
E + inhibitor-1E + inhibitor-2
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Competitive inhibition – Lineweawer-Burk plots
Kompetitív gátlás - Lineweaver - Burk ábrázolás
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0 0,05 0,1 0,15 0,2 0,25 0,3 0,35
1/[S]
1/v
Enzyme
Enzyme + Inhibitor 1
Enzyme + Inhibitor 2
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Competitive inhibition
KM value - increase, Vmax - constant
KI =/= KS
Inhibition depends on [S]/[I].
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Competitive inhibition
1/[S]
1/v
y=a*x+b
MaxMax
m
V
1
S
1*
V
K
v
1
MaxiMax
m
V
1
S
1*)]
K
I(1
V
K
v
1[
1/VMAX
Enzyme only
E + inhibitor1E + inhibitor2
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CH3 CH2 OH CH3 C
O
H
CH3 OH H C
O
H
CH2 OH
CH2 OH
CH2 C
O
HCH2 COOH
ethanol acetaldehyde
NAD+ NADH + H+
alcohol-dehydrogenase
etanol formaldehyde
NAD+ NADH + H+
ethylenglycol glycolic acid
NAD+ NADH + H+
alcohol-dehydrogenase
alcohol-dehydrogenase
Methanol
Ethylenegly
col
Ethanol
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Competitive inhibition
Acetylcholine esterase Acetylcholine Neostigmin Myasthenia gravisDOPA decarboxylase Dioxyphenyl-alanineMethyldopa HypertonyDihydrofolate reductaseDihidrofolate Aminopterine Leukemia
Xantine oxydase Xantine Allopurinol Gout
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Noncompetitive inhibition
+ S+ I
E + I ES E + P
EI EIS
S
S
X
+ S
+ P
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Noncompetitive inhibition
KM value is constant
VMax - decrease
Inhibitor-binding – different of substate binding site EIS complex – is inactive
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Nonkompetitive inhibition
Kontroll
I2
I1
1/[S]
1/v
1/Vmax
-1/KM
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Noncompetitive inhibition
E SH Cl Hg COO- Hg COO-SE+ HCl+
Metal / Enzyme + CN-, EDTA
Partially noncompetitive inhibitor
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Both KM & Vmax values - decrease
1/[S]
1/v
Enzyme alone
I1
Uncompetitive inhibition
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Inhibition of mixed typeInhibition of mixed type
KM - increase Vmax decrease
1/[S]
1/v
Control
I1
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Turnover number
Number of molecules converted by 1 molecule of enzyme
Vmax = k3*[Et]
k3 [sec-1] i.e.: 10-6 M carbonic anhydrase 0.6 M of H2CO3 in 1 secundum
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Enzyme Turnover number [sec-1]
Carbonic anhydrase 600.000,00
3-ketosteroid izomeráz 280.000,00
Acetylcholine esterase 25.000,00
Penicillinase 2.000,00
LDH 1.000,00
Chymotrypsin 100,00
DNA polimerase I 15,00
Tryptophane synthase 2,00
Turnover number
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Activity units
Enzyme activity units: 1 E (U): 1 mole/min 25 oC 1 Catal (SI): 1 mole/sec
Specific activity: mo/min/mg protein mol/sec/mg protein
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Enzyme activities – in everyday medical practice
Enzyme Measured value Normal value(l) Normal value (u).
Alk. phosphatase 175 U/l 98,00 290,00
CK 346 U/l 24,00 195,00
LDH 499 U/l 230,00 460,00
ASAT 21 U/l 1,00 46,00
ALAT 26 U/l 1,00 49,00
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Akut szívinfarktust követő CK-MB és LDH aktivitás szérumban
0
100
200
300
400
500
600
700
800
900
0 24 48 72 96
Az infarktust követő idő [óra]
Enz
im a
ktiv
itás
[rel
atív
U]
CK-MB
LDH ö
Enzyme activities – in everyday medical practice