METABOLISM OFNUCLEOTIDES

Tomáš Kuˇcera

Ústav lékaˇrské chemie a klinické biochemie 2. lékaˇrská fakulta, Univerzita Karlova v Praze

2013 NUKLEOTIDY

rocy

t e c

l

e e − − − h O O O N −O P O P O P O O O O O O H H H H OH OH

heterocycle = nucleobase the name is historic

pyrimidine purine nicotinamide, flavine PYRIMIDINEBASESANDNUCLEOSIDES PURINEBASESANDNUCLEOSIDES SOMELESSUSUALBASESANDNUCLEOSIDES

5-formylcytosine

6-methyladenine 4-methylcytosine FUNCTIONOFNUCLEOTIDES

precursors of DNA and RNA ATP, GTP, CTP, UTP, dATP, dGTP, dCTP, dTTP components of enzyme cofactors NAD(P), FAD, FMN, CoA [(P)APS – (phospho)adenosylphosphosulphate] macroergic “energy quanta” carriers ATP, GTP activated intermediates in biosyntheses UDP-sugars, CDP-diacylglycerols, S-adenosylmethionine second messengers in signal transduction cAMP, cGMP allosteric regulators ATP, ADP, AMP GAININGNUCLEOTIDES

pancreatic (deoxy)ribonucleases and intestinal polynucleotidases: NA → nucleotides nucleotidase of epithelial cells of the intestine: nucleotides → nucleosides in the intestinal epithelial cells, nucleosides are used intact hydrolyzed by nucleoside (phosphoryl)ases: nucleoside → base + pentose(-1-phosphate) + [phosphate] — salvage for the cells own need — transport to the blood about 5 % of digested nucleotides into the blood as bases and nucleosides low dietary uptake ⇒ need of biosynthesis PYRIMIDINENUCLEOSIDESBIOSYNTHESIS 1 PYRIMIDINENUCLEOSIDESBIOSYNTHESIS 2

UTP SYNTHESIS nucleosidmonophosphate- UMP + ATP kinase UDP + ADP

nucleosiddiphosphate- UDP + ATP kinase UTP + ADP

CTP SYNTHESIS REGULATION OF PYR. NUCLEOTIDESSYNTHESIS

carbamoylphosphate synthetase II activation by ATP, PRPP inhibition by UDP, UTP

OMP decarboxylase competitive inhibition by UMP (a little also CMP) SALVAGE PATHWAYS OF PYRIMIDINE NUCLEOTIDES

FORMATION OF NUCLEOSIDES

pyrimidine nucleoside Ura (Cyt) + ribose-1-phosphate phosphorylase U (C) + Pi

thymidine phosphorylase Thy + deoxyribose-1-phosphate T + Pi

FORMATION OF NUCLEOTIDES uridine-cytidine U (C) + ATP kinase UMP (CMP) + ADP

deoxythymidine dT + ATP kinase dTMP + ADP

deoxycytidine dC + ATP kinase dCMP + ADP PURINENUCLEOTIDESBIOSYNTHESIS 1 PURINENUCLEOTIDESBIOSYNTHESIS 2 FORMATION OF NTP

specific nucleoside monophosphate kinases no deoxyribose-ribose discrimination adenylate AMP + ATP kinase ADP + ADP

guanylate GMP + ATP kinase GDP + ADP

non-specific nucleoside diphosphate kinases nucleoside diphosphate GDP + ATP kinase GTP + ADP REGULATION OF PYR. NUCLEOTIDESSYNTHESIS

ribose phosphate pyrophosphokinase inhibition by ADP, GDP

amidophosphoribosyl transferase activation by PRPP inhibition by all A and G nucleotides, XMP

adenylosuccinate synthetasa IMP-dehydrogenase inhibition by GMP inhibition by AMP SALVAGE PATHWAYS OF PURINE NUCLEOTIDES

purines biosynthesis in the liver, brain, neutrophiles. . . nucleosides and free bases transported to other tissues for example lymphocytes use the salvage pathways as the main nucleotides source SALVAGE PATHWAYS OF PURINE NUCLEOTIDES LESCH-NYHANSYNDROME

uric acid overproduction gout symptomes neurological abnormalities, mental retardation, agressivity, self-mutilation

deficiency of HGPRT (X chromosome) ⇓ amidophosphoribosyltransferase activation ⇓ overproduction and increased degradation of purine nucleotides PURINE-NUCLEOTIDESCYCLE

combines biosynthetic and salvage enzymes of purine nucleotides metabolism anaplerotic pathway of the citrate cycle in skeletal muscles FORMATIONOFDEOXYRIBONUCLEOTIDES

ribonucleotide reductase + Fe3+,O2− radical mechanism reduction at the NDP phosphorylation level 3 allosteric sites activity specificity hexamerization

Substrate Effector of activity specificity no dATP NDP CDP ATP ATP or dATP UDP ATP ATP or dATP ADP ATP dGTP GDP ATP dTTP THYMIDINESYNTHESIS

dUTP + H2O dUMP + PPi dUDP + H2O dUMP + Pi dCMP + H2O dUMP + NH3 thymidylate synthase dTMP + ATP dTDP + ADP dTDP + ATP dTTP + ADP prevention of dU in DNA DEGRADATIONOFPURINENUCLEOTIDES DEGRADATION OF URIC ACID

HUMANSDONOTDEGRADEIT ⇒ GOUT elevated levels of uric acid in body fluids deposition in various tissues (joints, kidneys...)

deficient excretion Lesch-Nyhan syndrome deficiency of glucose-6-phosphatase

allopurinol DEGRADATIONOFPYRIMIDINENUCLEOTIDES NAD(P) SYNTHESIS NAD(P) FLAVINE “NUCLEOTIDES” SYNTHESIS THEEND Thank you for your attention!