nucleotide metabolism metabolism of purine...
TRANSCRIPT
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NUCLEOTIDE METABOLISM
Metabolism of purine nucleotides
Dr. Mária Sasvári
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p p p
Base(purine
or pirimidine)
Ribose or
deoxyR
Nucleotide (NMP, NDP, NTP)
Nucleoside
Nucleosides and nucleoties
e.g. adenosine
adenosine monophosphate (AMP) or: adenylate
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Liver
Blood
nucleosides
bases
urate
URINE
IntestineFood
RNA, DNA
polynucleotides
nucleotides
nucleosides
bases
EXTRAHEPATIC tissues
brain, RBC, lymphocytes)
“salvage reactions”
“de novo”
synthesis
nucleotides
nucleosides
bases
urate
DNA
RNA
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The origin of the ribose-P
PPP
ri-5-P
PRPP
Purine“de novo” and salvage reactions
Pyrimidine“de novo” synthesis
O-P P
1’
P-O-H2C
5’
O
glc-6-P
fru-6-PATP
AMP
PRPP synthetase
inhibitors: AMP, GMP
PRPP=phosphorybosyl pyrophosphate
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Purine nucleotide synthesis
IMP
ATP
ADP
AMP
GTP
GDP
GMP
“de novo”
synthesis
salvage
reactions
purine
bases
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IMP
The origin of the purine ring
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
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NH3+
9.
ri-5-P
Glu
Gln
PRA
(5’-phosphoribosyl-amine)
PRPP
1.
2.
GlycineATP
ADP + Pi
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
“de novo” purine synthesis
Gln PRPP amidotransferase
GAR synthetase
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GAR
(5’PR-Glycinamide)
3.
N10formyl H4F
H4F
“de novo” purine synthesis
NH
NH3+
9.O
ri-5-P
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
GAR transformylase
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NH
NH
O
ri-5-P
O
FGAR
(5’PR-formyl-glycinamide)
4.
Gln
Glu
ATP
ADP + Pi
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
“de novo” purine synthesis
FGAM synthetase
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HN
FGAM
(5’PR-formylglycinamidine)
5.
ATP
ADP + Pi
NH
NH
O
ri-5-P
H2NGln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
“de novo” purine synthesis
AIR synthetase
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N
N
ri-5-P
H2N
“de novo” purine synthesis
AIR
(5’PR-5-amino-imidazole)
6.
CO2
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
AIR carboxylase
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“de novo” purine synthesis
CAIR
(5’PR-4-Carboxy- 5-amino-imidazole)
7.
Asp
N
N
H2N
ri-5-P
ATP
ADP + Pi
-OOC
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
SAICAR synthetase
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“de novo” purine synthesis
SACAIR
(5’PR-succinyl-5-aminoimidazole-4-carboxamide)
8.fumarate
N
N
H2N
ri-5-P
O
HNszukcinil-
Adenilosuccinase (ASA)
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
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N
N
H2N
ri-5-P
O
“de novo” purine synthesis
ACAIR
(5’PR-5-aminoimidazole-4-carboxamide
9.
N10formyl H4F
H4F
H2N
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
AICAR transformylase
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“de novo” purine synthesis
FACAIR
5’PR-5-formamidoimidazole-4carboxamide)
10
. H2O
N
N
N
Hri-5-P
O
H2N
O
IMP
Gln
N10formyl H4F N10formyl H4F
Glycine
CO2
Asp
N
NN
N9.
IMP cyclohydrolase
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“de novo” purine synthesis
and the purine nucleotide cycle
IMP
ATP
ADP
AMP
GTP
GDP
GMP
IMP(6-oxo)
XMP(2,6,-dioxo)
GMP(2-amino-6-oxo)
AMP(6-amino)
Adenylosuccinate
Asp
GTP
GDP+Pi
fumarate
ASA
IMPDH
ADP+Pi
Gln
ATP
AMP DA
NAD+
H2O
NADH + H+
ASA: Adenylosuccinase
DA: deaminase
DH: dehydrogenase
AMP=adenylate or adenosine monophosphate
IMP=inosine monophosphate
XMP = xanthosine monophosphate
Adenylosuccinate
synthase
GMP
synthase
GluH2O
NH4+
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IMP
AMP
purin
nucleotide
cycle
urate
(urine)
AMPkinase
+ AMP
2 ADP
ATP AMP
low energy level
The purine nucleotide cycle
e.g. fructose intolerance
[AMP] hyperuricaemia
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Muscle
ATP
AMP glycolysis
IMP
NH3
+
inozine
Liver
NH3Inozine
urate
Muscle: high AMP DA level
urate
Myoadenylate deaminase def.:
Heavy exercise: NH3 , urate
cramps, NH3, urate is NOT elevated
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“de novo” purine synthesis
Summary
Multifunctional proteins
Carbon donors: „C1 units” (N10-formyl-TH4)
CO2
Glycine
N donors: Asp
Gln
Gly
No free purine base during synthesis
Energy: 6 ATP/IMP
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base nucleotide
adenine AMP
PRPP PPi
APRT
Purine salvage reactions
PRT (phosphorybosyl transferase)
IMP
GMPhypoxantine
guaninePRPP PPi
HPRT
IMP
ATP
ADP
AMP
GTP
GDP
GMP
“de novo”
synthesis
salvage
reactions
purine
bases
APRT=adenine phosphorybosyl transferase
HPRT=hypoxantine guanine phosphorybosyl transferase
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The Lesh-Nyen syndrome
Linked to X-chromosome
mental retardation
self-mutilation
aggression
hyperuricemia
HPRT deficiency:
GTP level of the basal ganglions are low
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IMP
ATP
ADP
AMP
GTP
GDP
GMP
IMP
ATP
ADP
AMP
GTP
GDP
GMPRegulation
++“salvage” “salvage”
- -
PRPP
Gln PRPP amidotransferaseInhibitors: IMP, GMP, AMP
Activator: PRPP
Also see before: PRPP synthetase inhibitors (AMP, GMP)
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PNP (purine nucleoside
phosphorylase)
Catabolism of the purine nucleotides
adenosine (6-amino)
inosine (6-oxo)
hypoxantine
Br -p
Br
H2O
NH3
AMP GMP
guanosine
Pi Pi
guanine
ri-1-P
Pi
ri-1-P
Pi
5’nucleotidease
ADA
adenosine deaminase
B
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Mechanism:
Reason:
Symptoms:
ADA / PNP / (ADA + PNP)Severe combined immunodeficiency
Immunodeficiency “NON-HIV AIDS”
T cell deficiency
adenosine dATP (ATP)
dATP inhibition of ribonucleotide reductase
inhibition of DNA synthesis
inhibition of cell division
Treatment: PEG - ADA enzyme teraphy,
Enzyme deficiency:
Gene therapy
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H2O + O2
H2O2
H2O + O2
H2O2
Xantine oxidase
xantine
(2,6-dioxopurine)
H2O
NH3
guanase
hypoxantine
(6-oxo-purine)
Purine salvage reactions
guanine
(2-oxo-6-amino-purine)
urate
(2,6,8-trioxopurine)
URINE
E
x
c
r
e
t
i
o
n
Catabolism of
the purine
nucleotides
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Hyperuricemia (gout)
Symptoms: urate crystals on the napkin (Lesh-Nyan)
Na-urate crystals stones
urate in soft tissues and joints: “tophi”
inflammation reaction, pain
Acute gouty arthritis
chronic gouty arthritis
Reason: Urate has low solubility
(especially at acidic pH )
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Medication of gout: allopurinol
allopurinol oxopurinol
hypoxantine xantineXantine oxidase
Competitive inhibitors
Hypoxantine and xantine in urine (better solubility )
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Origins of Hyperuricemia
1. PRPP overproduction• as a consequence of mutation
at the allosteric site of PRPP synthase,
the enzyme cannot be inhibited
•overproduction of ribose-5-P PPP
ri-5-P
PRPP
gl-6-P
fr-6-P
e.g. gl-6-phosphatase deficiency
(Von Gierke disease)
Gl- 6-P fr- 6-P ri- 5-P
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2. Absence of purine salvage reactions
e.g. HPRT deficiency
Decreased adenine, guanine reutilization
increased excretion
Origins of Hyperuricemia
IMP
ATP
ADP
AMP
GTP
GDP
GMP
“de novo”
synthesis
salvage
reactions
purine
bases
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3. Low ATP level, disturbed ATP metabolism
• heavy exercise
• fructose intolerance (phosphate trap)
Origins of Hyperuricemia
4. Secondary reasons:
• tissue damage
• cancer, chemotherapy (Tumour lysis syndrome)
DNA breakdown
overproduction of purines