Metabolism of purines and pyrimidines Vladimíra Kvasnicová The figure was found at (Jan 2008)

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2 PURINE BASES

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2 PYRIMIDINE BASES

Structure of purine and pyrimidine nucleotides nucleotide = ester of phosphoric acid and a nucleoside nucleoside = N-containing base + monosaccharide  -N-glycosidic bond between base and saccharide nucleotide bases: aromatic heterocycles  purines: pyrimidine + imidazol ring  pyrimidines: pyrimidine ring

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2 ribonucleoside deoxyribonucleoside N-glycosidic bond

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2 ribonucleosides deoxyribonucleoside

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2 Ribonucleotides * N-glycosidic bond * ester bond * anhydride bond

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2 ribonucleotide deoxyribonucleotide

Classification of nucleotides purine nucleotides: contain adenine, guanine, hypoxanhine or xanthine pyrimidine nucleotides: contain cytosine, uracil or thymine ribonucleotides (saccharide = ribose) deoxyribonukleotidy (saccharide = deoxyribose)  formed by reduction of ribonucleoside diphosphates (NADPH)

The figure was found at (Jan 2007) 3´-phosphoadenosine-5´-phosphosulfate (PAPS) used as the sulfate donor in metabolic reactions (sulfatation)

Properties of nucleotides strong absorption of UV radiation (260 nm) purines are less stable under acidic conditions than pyrimidines polar terminal phosphate groups  alternative names: adenylate or adenylic acid,...

Purine and pyrimidine nucleotides essential for all cells mainly 5´-nucleosidedi and triphosphates ribonucleotides: concentration of a sum of them is constant (mM), only their ratio varies (main ribonucleotide of cells: ATP) deoxyribonucleotides: their concentration depends on a cell cycle (µM)

Nucleotides in a metabolism 1) energetic metabolism ATP = principal form of chemical energy available to cells – „as money of the cell“ (30 kJ/mol / spliting off phosphate)  phosphotransferase reactions (kinases)  muscle contraction, active transport 2) monomeric units of RNA and DNA  substrates: nucleoside triphosphates

The figure was adopted from Harper´s Illustrated Biochemistry 26 th ed./ R.K.Murray; McGraw-Hill Companies, 2003, ISBN Synthetic analogs of purines and pyrimidines are used in chemotherapy

The figure was found at (Jan 2008) Cyclic adenosine monophosphate (cAMP) 3) physiological mediators cAMP, cGMP („second messengers“)

4) components of coenzymes  NAD +, NADP +, FAD, CoA The figures were found at a (Jan 2008)

5) activated intermediates  UDP-Glc, GDP-Man, CMP-NANA  CDP-choline, ethanolamine, diacylglycerol  SAM  methylation  PAPS  sulfatation 6) allosteric efectors  regulation of key enzymes of metabolic pathways

PRDP = 5-fosforibosyl-1-diphosphate The figure was found at angers.fr/~jaspard/Page2/COURS/2N2NH3aaetUree/2Figures/9AAaromatiques/8PRPP.gif (Jan 2008) angers.fr/~jaspard/Page2/COURS/2N2NH3aaetUree/2Figures/9AAaromatiques/8PRPP.gif = the substrate for synthesis of both purines and pyrimidines

PRPP = 5-phosphoribosyl-1-diphosphate its synthesis is a key reaction of synthesis of the nucleotides PRPP-synthetase is regulated by feed back inhibition by nucleoside di- and triphosphates precursors:* ribose-5-phosphate (from HMPP) * ribose-1-phosphate (phosphorolysis of nucleosides)

function:  regulation of nucleotide synthesis  substrate of nucleotide synthesis The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2 PRPP = PRDP

Synthesis of purine nucleotides de novo = new building of a nucleotide rings salvage reactions = synthesis from bases or nucleosides  less energy need than for de novo synthesis  they inhibit de novo synthesis  substrates: a) base (adenine, guanine, hypoxanthine) PRPP b) ribonucleosides ATP

The figure was found at (Jan 2007) Synthesis of purine nucleotides CYTOPLASMCYTOPLASM

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2 AMP GMP IMP

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2

The figure was found at (Jan 2008) Bacteria can synthesize the folate: sulfonamides are analogs of PABA → bacteriostatic effect Folate is a vitamin – it is not synthesized in human cells

The figure was found at (Jan 2008) cytostatics

The figure was found at (Jan 2008) Activation of folate (reduction) Dihydrofolate reductase can be inhibited by Methotrexate

The figure was found at (Jan 2008) Derivatives of tetrahydrofolate

The figure was found at (Jan 2008) Serin is the principal donor of methylene group

The figure was found at (Jan 2008) Folate in a metabolism

Synthesis of purine nucleotides de novo (I) high consumption of energy (ATP) cytoplasm of many cells, mainly in the liver substrates:* 5-phosphoribosyl-1-diphosphate (= PRDP = PRPP) * amino acids (Gln, Gly, Asp) * tetrahydrofolate derivatives, CO 2 coenzymes: * tetrahydrofolate (= THF) * NAD +

important intermediates:  5´-phosphoribosylamine  inosine monophosphate (IMP) products: nucleoside monophosphates (AMP, GMP) interconversion of purine nucleotides:  via IMP = common precursor of AMP and GMP (inosine monophosphate: base = hypoxanthine) Synthesis of purine nucleotides de novo (II)

Synthesis of pyrimidine nucleotides de novo = new building of a nucleotide rings salvage reactions = synthesis from bases or nucleosides  substrates: a) * base (not cytosine) * PRPP b) * ribonucleosides * ATP

The figure was found at (Jan 2007) Synthesis of pyrimidine nucleotides CYTOPLASMCYTOPLASM mitochondrion

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley ‑ Liss, Inc., New York, ISBN 0 ‑ 471 ‑ ‑ 2

Synthesis of thymidine monophosphate

Synthesis of pyrimidine nucleotides de novo (I) cytoplasm of cells (exception: one enzyme is found at mitochondria /dihydroorotate-DH) substrates:* carbamoyl phosphate (Gln,CO 2,2ATP) * aspartate * PRPP * methylene-THF (only for thimidine) Karbamoyl phosphate is formed in urea synthesis as well (only in mitochondria of hepatocytes)

important intermediates: * orotic acid (pyrimidine derivative) * orotidine monophosphate (OMP) * uridine monophosphate (UMP) products:* cytidine triphosphate ( from UTP) * deoxythimidine monophosphate ( from dUMP) Synthesis of pyrimidine nucleotides de novo (II)

The figure was found at (Jan 2008) Synthesis of 2-deoxyribonucleotides The reaction is catalyzed by ribonucleotide reductase NADP + NADPH+H + protein

Regulation of nucleotide synthesis PRPP-synthetase is inhibited by both purine and pyrimidine nucleoside di- and triphosphates nucleotide synthesis: feed back inhibition nucleoside diphosphate reductase: activated by nucleoside triphosphates, inhibited by deoxyadenosine triphosphate (dATP)

The figure was found at (Jan 2008) Regulation of synthesis of purine nucleotides

The figure was found at (Jan 2008) Regulation of synthesis of pyrimidine nucleotides

Regulation of nucleotide synthesis regulatory enzymeactivationinhibition glutamine-PRPP amidotransferase (purines)  PRPP  IMP, GMP, AMP (allosteric inhibition) carbamoylphosphate synthetase II = cytosolic (pyrimidines)  PRPP  ATP  UTP

Degradation of purines and pyrimidines exogenous: mostly not used for resynthesis endogenous:  enzymes * nucleases (split off nucleic acids) * nucleotidases (...nucleotides) * nucleoside phosphorylases (nucleosides) * deaminase (adenosine) * xanthinoxidase (substrates: hypoxanthine, xanthine) inhibited by allopurinol (pharmacology)

The figure was found at (Jan 2008) Degradation of purines

URIC ACID keto and enol form salts of uric acid = urates pH of blood: mononatrium urate

The figure was adopted from Color Atlas of Biochemistry / J. Koolman, K.H.Röhm. Thieme ISBN

Degradation of pyrimidines

SUMMARY:  purines → NH 3, uric acid – it has antioxidative properties (partially excreted with urine; failure: hyperuricemia, gout) physiological range: serum220 – 420 µmol/l (men) 140 – 340 µmol/l (women) urine0,48 – 5,95 mmol/l  pyrimidines: C, U →  -alanine, CO 2, NH 3 T →  -aminoisobutyrate, CO 2, NH 3 The figures were adopted from and (Jan 2008) free radicals

Principal differences between metabolism of purines and pyrimidines purinespyrimidines formation of N-glycosidic bond in 1 st step of their biosynthesis (PRDP is the 1 st substrate) a heterocyclic ring is formed first, then it reacts with PRDP location of biosynthesis cytoplasmcytoplasm + 1 enzyme is in a mitochondrion products of degradation uric acid (poor solubility in H 2 O), NH 3 CO 2, NH 3,  -AMK (soluble in H 2 O)