university of veterinary medicine department of physiology and … · 2019-10-31 · urate kidney...
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Nucleotide metabolism
University of Veterinary Medicine
Department of Physiology and Biochemistry
DNA is stored in the nucleus of
eucaryotes, RNA found in cytoplasm or
ribosomes
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Structure of
nucleic acids
Structure of nucleotides and nucleosides
• Nucleotide = base + pentose + phosphate
N-glycosidic bond
(Phosphate) ester
bond
Nucleoside =
base + pentose
Pentose: ribose or
(2-)deoxy-ribose
• Nucleotide = base + pentose + phosphate
• Bases:
– Purine bases
purine
adenine
(6-amino-purine)
guanine
(2-amino-
6-oxo-purine)
Structure of purine nucleotides
(purine bases)
Bound to ribose (RNA)
or deoxyribose (DNA)
• Nucleotide = base + pentose + phosphate
• Bases:
– Pyrimidine bases pyrimidine
cytosine
(2-oxo-
4-amino-pyrimidine)
uracil
(2,4-dioxo-pyrimidine)
Keto-enol
tautomery(example: uracil)
thymine
(5-methyl-
uracil)
Structure of pyrimidine nucleotides
(pyrimidine bases)
Structure of nucleotides• Uracil: bound only to ribose
• Thymine: bound only to deoxyribose
• Cytosine: bound to ribose or deoxyribose
Purine nucleosides:
(deoxy)adenosine, (deoxy)guanosine
Pyrimidine nucleosides:
uridine, (deoxy)cytidine, deoxythymidine
Nucleotides:
nucleoside + mono-/di-/triphosphate:
(d-)adenylic acid, (d-)guanylic acid, uridylic
acid, (d-)cytidylic acid, d-thymidylic acid
Synthesis of purine nucleotides (de novo)
glucose glucose 6-
phosphate
hexokinase
ATP ADP
ribose 5-phosphatepentose phosphate
pathway
PRPP
synthetase
ATP
AMP
5-phosphoribosyl-1-pyrophosphate (PRPP)
5-phosphoribosyl-amine
PRPP amidotransferase*glutamine
glutamate
P – P
5-phosphoribosyl-amine
glycine
N10-formyl-FH4 (FH4=tetrahydro folic acid)
FH4
glutamine
glutamate
HCO3-
H2O
aspartate
fumarate
N10-formyl-FH4
FH4
inosine monophosphate (IMP)
HCO3-
Asp
formyl
Gly
formyl
Gln
phosphoribosyl-amine
inosine monophosphate (IMP)
xanthosine monophosphate
IMP
dehydrogenase H2O
NAD+
NADH+H+
adenylosuccinate synthetase
adenylosuccinate
aspartate
GTP GDP
+Pan
glutamine
glutamate
ATP
AMP + PPGMP synthetase fumarate
guanosine monophosphate (GMP)
adenosine monophosphate (AMP)
adenylosuccinate
lyase
ribose
ribose
ribose
ribose
ribose
guanosine monophosphate (GMP) adenosine monophosphate (AMP)
ATP
ADP
ATP
ADP
nucleotide kinase nucleotide kinase
guanosine diphosphate (GDP) adenosine diphosphate (ADP)
nucleoside
diphosphate kinase
ATP
ADP
guanosine triphosphate (GTP)
Pin
oxidative
phosphorylation
substrate level
phosphorylation
adenosine triphosphate (ATP)
• Allosteric regulation:
– „+” effector: PRPP
– „-” effector: IMP, GMP, AMP
• Localization: each cell type, cytosol
• Needs lots of energy! (8 ATP)
PRPP amidotransferase*
AMPnucleotidase
Pin
adenosine
adenine
Pin
ribose-1-P
nucleoside
phosphorylase
H2O
NH3
adenine
deaminase
hypoxanthine
Degradation of purine nucleotides
AMP
Hypoxanthine
hypoxanthine
H2O
FAD
FADH2
xanthine oxidase
xanthine
H2O
FAD
FADH2
xanthine oxidase
uric acid
CO2
uricase
allantoine
Excreted by the
urine in primates,
birds and reptiles
Excreted by the urine in other species
(dog, cat, horse, ruminants, pig etc.)
Exception: dalmatian dog!
2H2O+O2
H2O2
GMPnucleotidase
Pin
guanosine
guanine
Pin
ribose-1-P
nucleoside
phosphorylase
H2O
NH3
guanine
desaminase
xanthine
uric acid
allantoine
guanine
GMP
xanthine
• Localization: each cell type, cytosol
– Only until uric acid!
• Uric acid → allantoine reaction only in the liver
– Allantoine is excreted by the urine
• Clinical relevance:
– Uric acid is very bad soluble in water precipitation in
joints, serosal membranes, kidneys inflammation
gout / uricosis
– Treatment: allopurinol
• Similar structure to hypoxanthine competitive
inhibition of xanthine oxidase
Uricosis: precipitated uric acid crystals in the kidney of a snake
Photo by Dr. János Gál
Gout in human
Visceral gout in poultry
Gout in parrot
Uricosis:
tophus-formation (H.E.)
Urate crystals
Proliferating cells
Urate kidney stones of Dalmatian dog
• Transport of uric acid happens by 2 different
transport processes in the liver:
• 80% fast Transport
20% slow Transport
• Dalmatian: fast transport gene of uric acid in the
liver has been mutated uricase is active in the
liver, but no uric acid uptake Excretion: mostly
uric acid, but also some allantoine uric acid
can be precipitated in the joints (gout) or kidney
(kidney stones).
Urolithiasis in dalmatian dog: urate crystals in the urine sediment
Urolithiasis in dalmatian dog: ectomised stones after surgery
• Nucleotide = base + pentose + phosphate
• Bases:
– Pyrimidine bases pyrimidine
cytosine
(2-oxo-
4-amino-pyrimidine)
uracil
(2,4-dioxo-pyrimidine)
Keto-enol
tautomery(example: uracil)
thymine
(5-methyl-
uracil)
Revision: structure of nucleotides
HCO3-
carbamoyl
phosphate
synthetase II.
glutamineglutamate
2 ATP2 ADP +Pin
carbamoyl-P aspartate
aspartate
transcarbamoylase
N-carbamoyl
aspartate
*
dihydroorotase
dihydroorotate
*
Synthesis of pyrimidine nucleotides
(de novo)
Pin
H2O
dihydroorotate
NAD+
NADH+H+
dihydroorotate
dehydrogenase
orotateorotate phosphoribosyl
transferase
PRPP
P-P
orotidylateorotidylate decarboxylase
CO2
uridine monophosphate
(UMP)
dihydroorotate
NAD+
NADH+H+
dihydroorotate
dehydrogenase
orotateorotate phosphoribosyl
transferase
PRPP
P-Pin
orotidylateorotidylate decarboxylase
CO2
uridine monophosphate
(UMP)
UMP kinase
ATP ADP
UDP
nucleoside
diphosphate
kinase
ADP
ATP
UTP
CTP synthetase
ADP +Pan
ATP
glutamate
glutamine
cytidinetriphosphat
(CTP)
*
• Localization: each cell type, cytosol
• Regulation:
Carbamoylphosphate synthetase II. (eukaryotes)– Positive allosteric effector: PRPP
– Negative allosteric effector: UTP
Aspartate transcarbamoylase (prokaryotes)
CTP-synthetase– Positive (+)allosteric effector: GTP
– Negative (-)allosteric effector: CTP
• Needs lots of energy! (7 ATP)
*
*
*
Localization and regulation
CMPCMP-deaminase
H2O NH3
UMPnucleotidase
Pin
uridine
Nucleoside
phosphorylase
Pan ribose-1-P
uracil
NADH+H+
NAD+
Pyrimidine dehydrogenase
dihydro-uracil
H2O
ureido-propionateureido-
propionase
NH3CO2
β-alanine
CO2
NH3
acetate
- Localization: each cell type, cytosol
- Regulation: depends on the amount of
nucleotides to be degradated
HS-CoA
dihydro-
pyrimidinase
Degradation of pyrimidine nucleotides
Resynthesis of nucleotides (salvage pathway)
Each nucleotide: nucleoside
ATP ADP
nucleoside kinasenucleotide
Purin nucleotides:adenine
PRPP PPin
Adenine-
phosphoribosyltransferaseAMP
guanine
hypoxanthine
guanine
xanthine
GMP
IMP
GMP
XMP
PRPP PPin
PRPP PPin
hypoxanthine-guanine-
phosphoribosyltransferase
(HGPRT)
xanthine-guanine-
phosphoribosyltransferase
(XGPRT)
eukaryotes:
prokaryotes:
Synthesis of deoxyribonucleotides
ADP
GDP
CDP
UDP
dADP
dGDP
dCDP
dUDP
ribonucleoside-diphosphate-reductaseH2O
FAD FADH2
thioredoxin-redctase
NADPH+H+ NADP+
Instead of
thioredoxin
could be
glutathione
also!
ATP ADP
dATP
dGTP
dCTP
dUTP
dUTPase/ dUTP-
phosphataseP-Pan
dUMP
dTMP
thymidilate synthase
N5,N10-methylene-
FH4
FH2
ATP
ADP
dTDP
ADP ATP
dTTP
nucleoside
diphoshosphate
kinase
Ascorbic aciddehydroascorbic
acid
Cobalamin is
needed also!
thioredoxin thioredoxin
Degradation of deoxyribonucleotides
• Differences compared to the degradation of ribonucleotides:– Nucleoside phosphorylase releases deoxy-ribose-1-
P from deoxyribonucleosides
– At purine bases: no differences in steps of degradation
– At pyrimidine bases: differences in steps of degradation are as follows:
• Deoxythymidine has one more methyl group, that s why instead of ureidopropionate ureidoisobutyrate will be produced. The endproduct is instead of β-alanine β-amino-isobutyrate
• Localization: in each cell type, cytosol
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