Presentation is loading. Please wait.

Presentation is loading. Please wait.

1 NUCLEOTIDE METABOLISM Metabolism of pyrimidine nucleotides NUCLEOTIDE METABOLISM Metabolism of pyrimidine nucleotides Prof. Mária Sasvári Gergely Keszler.

Similar presentations


Presentation on theme: "1 NUCLEOTIDE METABOLISM Metabolism of pyrimidine nucleotides NUCLEOTIDE METABOLISM Metabolism of pyrimidine nucleotides Prof. Mária Sasvári Gergely Keszler."— Presentation transcript:

1 1 NUCLEOTIDE METABOLISM Metabolism of pyrimidine nucleotides NUCLEOTIDE METABOLISM Metabolism of pyrimidine nucleotides Prof. Mária Sasvári Gergely Keszler 2009.

2 2 The structure of nucleobases N-containing, heterocyclic aromatic compounds; substituted purine or pyrimidine rings RNA DNA

3 3 BLOOD Pyrimidine nucleotides cytidin e uridine PRPP “de novo” synthesis CTP  UTP Catabolism CO 2, NH 3,  -alanine  CoA salvage reactions   CMP    UMP  dTTP

4 4 UTP  UDP  UMP CTP “de novo” synthesis Asp Gln CO 2 CAD Py 1-3 H 2 OA mito Py 4 UMP-S Py 5,6 OA PYRIMIDINE nucleotide synthesis nucleosides salvage reactions

5 5 CO 2 2. Asp “de novo” PYRIMIDINE synthesis 1. Glu Gln 2 ATP 2 ADP + P i NH 2 C OO - P carbamoyl-P Carbamoyl-P synthetase II (CPSII) C Py1 Asp transcarbamoylase A Py2

6 6 “de novo” PYRIMIDINE synthesis 3. Dihydroorotase D Py3 NH 2 C O NHNH carbamoyl-Asp COO - HN O NHNH Dihydroorotate (H 2 OA) COO - O H2OH2O

7 7 OA “de novo” PYRIMIDINE synthesis Dihydroorotate dehydrogenase Py4 HN O NHNH orotate (OA) COO - O 4. NADH + H + NAD +

8 8 UMP-S (synthase) Py5 Py6 “de novo” PYRIMIDINE synthesis Orotate phosphoribosyl transferase 5. PP i PRPP HN O N COO - O R- P Orotidylate (OMP) UMP 6. CO 2 OMP decarboxylase

9 9 UTP  UDP  UMP 7. Pyrimidine monophosphate kinase ADP ATP UMP UDP 8. Pyrimidine diphosphate kinase ADP ATP UTP (2,4-dioxo) CTP 9. CTP synthetase Glu Gln CTP (2-oxo-4 amino) ADP ATP

10 10 UMP Regulation of PYRIMIDINE “de novo” synthesis Regulation of PYRIMIDINE “de novo” synthesis CAD Py 1-3 CAD complex: a single polypeptide three active centers + allosteric sites UTP + PRPP

11 11 Comparison of CPS I and II isoenzymes CPSI CPSII role urea cycle de novo pyrimidine biosynthesis localization mitochondrial cytosolic N-donor free NH 3 glutamine regulation + N-acetyl-glutamate + PRPP, - UTP

12 12 Orotic aciduria 1. UMP-S deficiency 2. Inhibition of UMP-S  Allopurinol treatment (gout)  6-azauridine treatment (tumor) 3. Ornitine transcarbamoylase deficiency (urea cycle): NH 3  CP  Type II hyperammonemia, carbamoyl P (CP) accumulation CAD can use the leaking CP  orotic acid overproduction  orotic aciduria treatment: oral uridine Main reasons of orotic aciduria

13 13 citidin uridin   CMP    UMP SALVAGE Nucleoside  nucleotide SALVAGE Cytidylate deaminase UMP B r -p B r uridine cytidine CMP Uridine/cytidine kinase H2OH2ONH 3 ATP ADP ATP ADP

14 14 B r -p UMP ( TMP ) CMP uridine (thymidine)cytidine B r PiPi PiPi 5’nucleotidase cytidine deaminase H2OH2ONH 3 CATABOLISM Nucleotide  Nucleoside CATABOLISM cytidine uridine   CMP    UMP 

15 15 cytidine deaminase pyrimidine nucleoside phosphorylase dihydropyrimidine dehydrogenase dihydropyrimidinase ureidopropionase Coenzyme A

16 16 β-D-ribofuranose (in RNA) 2’-deoxy-β-D-ribofuranose (in DNA) In cells, deoxyribonucleotides are synthesised from ribonucleotides by the ribonucleotide reductase enzyme Formation of deoxynucleotides NADPH + H + NADP + H2OH2O

17 17 The ribonucleotide reductase reaction (RR) RR S S SHSH SHSH TR S S SHSH SHSH FADH 2 FAD NDP dNDP TR: thioredoxin reductase or: glutaredoxin reductase (glutathion) NDP: UDP/ADP/GDP/CDP NADPH+ H + NADP + H2OH2O

18 18 Mechanism of the RR reaction ribonucleotide reductase

19 19 The RR is a dimer R1 – catalytic subunit constitutive expression R2 – regulatory subunit induced in the S-phase RR is active in dividing cells!

20 20 Allosteric REGULATION 1. dATP: complete inhibition 2. Regulation of the ratio Substrates: CDP UDP GDP ADP Products: dCTP dTTP dGTP dATP + + dUDP  dUMP    dCDP 

21 21 Synthesis of thymine nucleotides Folate antagonists (chemotherapy!) dTTPDNA UMP UDP dUDP

22 22 5-FU, a potent inhibitor of thymidylate synthase 5-fluoro-uracil (5-FU) inhibitor of thymine synthesis – WHY?? used to treat solid tumors (pancreas, lung, colon)

23 23 Inhibition of the folate synthesis: antibacterial effect Human: folic acid is a vitamin Bacteria: synthesis of folate can be selectively inhibited sulphonamides folic acid

24 24 The role of folate and vitamin B 12 in DNA synthesis and cell division in DNA synthesis and cell division The role of folate and vitamin B 12 in DNA synthesis and cell division in DNA synthesis and cell division HomoCys Met THF CH 3 -THF CH 2 -THF Gly Ser dUMP  dTMP purine synthesis Cell division SAM SAH -CH 3 adenosine B 12     “methyl trap”    B 12 /folate deficiency: pernicious anemia oxidative stress atherosclerosis folate cycle SAM/SAH cycle

25 25 Folate deficiency – megaloblastic anemia

26 26 Vitamin B 12 (cobalamin) deficiency Methylmalonic aciduriaMegaloblastic anemia (Pernicious anemia) nerve degeneration paralysis and death (B12 is needed for myelin synthesis) Anemia is due to impaired dTTP synthesis for DNA replication in hematopoetic precursor cells might be due to achlorhydria (chronic gastritis, no IF production) treatment: parenteral administration of B 12

27 27 “Salvage” reaction of deoxynucleosides “Salvage” reaction of deoxynucleosides lymphoid specific Deoxycytidine kinase (dCK) Broad substrate specificity dAdo, dGuo, dCyd Analogues of deoxynucleotides: antileukemic agents purine and pyrimidine analogues dCyd  dCMP ATPADP Substrates: dThd  dTMP ATPADP Thymidine kinase (dTK)

28 28 Purine analogues 6-mercaptopurine 8-azaguanine 2-chloro-2’-deoxyadenosine (CdA, Cladribine ® ) Hairy cell leukemia (HCL)

29 29 Pyrimidine analogues containing sugar derivatives arabinosyl-cytosine (araC; for treating AML) 2’, 3’-dideoxy-cytidine 2’-deoxy-2’, 2’- -difluorocytidine (dFdC, Gemcitabine)

30 30 S-phase dependent enzyme Thymidine kinase (dTK) dThd  dTMP ATPADP Human dTK: narrow substrate specificity Herpes Simplex Virus : HSV- dTK: wide substrate specificity  Antiviral medication (Acyclovir) Suicide gene therapy (Gancyclovir, AIDS) “Salvage” reaction of deoxynucleosides “Salvage” reaction of deoxynucleosides

31 31 AcyclovirStavudine Didanosine Antiviral nucleoside analogues 9-hydroxyethoxy- methyl guanine, an acyclic nucleoside inhibition of viral DNA (RNA) replication herpes viruses, HIV inhibitors of retroviral reverse transcriptase

32 32 „de novo” synthesis of purine- pyrimidine nucleotides „free” (no sugar) purine/pyrimidine ring containing intermedier NO YES (orotic acid) PRPP is an allosteric activator YES C 1 -TH 4 donor YESNO (except thymidine!) role of Asp N donorincorporates origin of amino groups Asp, Gln Gln origin of the atoms in the ring Gly, Asp, Gln, C 1 -THF, CO 2 Asp CO 2, NH 3 (Gln, Glu)

33 33 „salvage” pathway of purine- pyrimidine nucleotides mainly from bases through PRPP reaction YES NO PRPP is necessary YESNO mainly from nucleosides NOYES

34 34 Catabolic pathway of purine- pyrimidine nucleotides N of rings will be excreted YES NO amino groups saved YES diseases hyperuricemiaorotic aciduria


Download ppt "1 NUCLEOTIDE METABOLISM Metabolism of pyrimidine nucleotides NUCLEOTIDE METABOLISM Metabolism of pyrimidine nucleotides Prof. Mária Sasvári Gergely Keszler."

Similar presentations


Ads by Google