nucleotide metabolism metabolism of purine...

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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


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


NH

NH3+

9.O

ri-5-P

Gln


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


Glycine

CO2

Asp

N

NN

N9.


FGAM synthetase

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HN

FGAM

(5’PR-formylglycinamidine)

5.

ATP

ADP + Pi

NH

NH

O

ri-5-P

H2NGln


Glycine

CO2

Asp

N

NN

N9.


AIR synthetase

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N

N

ri-5-P

H2N


AIR

(5’PR-5-amino-imidazole)

6.

CO2

Gln


Glycine

CO2

Asp

N

NN

N9.

AIR carboxylase

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CAIR

(5’PR-4-Carboxy- 5-amino-imidazole)

7.

Asp

N

N

H2N

ri-5-P

ATP

ADP + Pi

-OOC

Gln


Glycine

CO2

Asp

N

NN

N9.

SAICAR synthetase

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SACAIR

(5’PR-succinyl-5-aminoimidazole-4-carboxamide)

8.fumarate

N

N

H2N

ri-5-P

O

HNszukcinil-

Adenilosuccinase (ASA)

Gln


Glycine

CO2

Asp

N

NN

N9.

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N

N

H2N

ri-5-P

O


ACAIR

(5’PR-5-aminoimidazole-4-carboxamide

9.

N10formyl H4F

H4F

H2N

Gln


Glycine

CO2

Asp

N

NN

N9.

AICAR transformylase

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FACAIR

5’PR-5-formamidoimidazole-4carboxamide)

10

. H2O

N

N

N

Hri-5-P

O

H2N

O

IMP

Gln


Glycine

CO2

Asp

N

NN

N9.

IMP cyclohydrolase

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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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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


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)


4. Secondary reasons:

• tissue damage

• cancer, chemotherapy (Tumour lysis syndrome)

DNA breakdown

overproduction of purines

nucleotide metabolism metabolism of purine...

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