chapter核苷酸代謝

1、Nucleotides metabolism【目的與要求】記住嘌呤核苷酸有兩條合成途徑。結(jié)合嘌呤核苷酸結(jié)構(gòu)與從頭合成途徑，說(shuō)出嘌呤核苷酸各元素或組件的材料來(lái)源。熟記二磷酸核苷還原生成脫氧嘌呤核苷酸。寫出與嘌呤核苷酸補(bǔ)救合成有關(guān)的酶的名稱、功能、酶缺陷相關(guān)的疾病 結(jié)合嘌呤核苷酸合成途徑、調(diào)節(jié)，熟記嘌呤核苷酸抗代謝藥物作用機(jī)理及臨床意義 記住嘌呤核苷酸體內(nèi)分解代謝終產(chǎn)物-尿酸及其與醫(yī)學(xué)的關(guān)系 熟記嘧啶核苷酸從頭合成的原料及合成調(diào)節(jié)。說(shuō)出嘧啶核苷酸補(bǔ)救合成所需的酶及其催化的反應(yīng)。明白嘧啶核苷酸抗代謝藥物作用機(jī)理，記住嘧啶核苷酸分解代謝產(chǎn)物名稱 8.1 Purine metabolism -8.1.1

2、 The Biosynthesis of Purines -8.1.2 Purine Salvage -8.1.3 De-oxyribonucleotide Synthesis -8.1.4 Purine Degradation 8.2 Pyrimidine metabolism -8.2.1 Biosynthesis of Pyrimidines -8.2.2 Pyrimidine DegradationOutlineBiological Roles of Nucleotides Monomeric units of nucleic acids * “ Energy currency”(AT

3、P) * Regulation of physiological processes Adenosine controls coronary(冠脈) blood flow cAMP and cGMP serve as signaling molecules Precursor function (GTP to tetrahydrobiopternin) Coenzyme components ( 5-AMP in FAD/NAD+) Activated intermediates: UDP-Glucose Allosteric effectors- regulate themselves an

4、d othersDeoxyribonucleotide umolfoodprotein nuclear acid (RNA and DNA) (intestine)Endonucleases(phosphodiesterase) mononucleotideNucleotidase(phosphoesterase) nucleosidePhosphatenucleosidaseRibose or ribose-1-phosphatebaseNuclear acid digestionUric acid (purines)-ureidopropionate( primidines)RNaseDN

5、ase(stomach)ribonucleotide mmol(戊糖代謝)excrete 思 考？8.1.1 Nucleotide Biosynthesis For both purines and pyrimidines there are two means of synthesis - de novo (from bits and parts) - salvage (recycle from pre-existing nucleosides,and bases) Ribose generates energy, but purine and pyrimidine rings do not

6、 Nucleotide synthesis pathways are good targets for anti-cancer/antibacterial strategiesBases/Nucleosides/Nucleotides BaseBase + Sugar=NucleosideBase + Sugar + Phosphate=NucleotideAdenineDeoxyadenosineDeoxyadenosine 5-triphosphate(dATP)The Pyrimidine RingThe Purine RingPurineCNCHCCNNNHCHNH2CNCCCNNNH

7、CHOH2N26腺嘌呤腺嘌呤A鳥嘌呤鳥嘌呤GPyrimidineCHNCCCHNHCH3OOCytosineNH2OCCHNCHCHNHThymineDe novo purine biosynthesis John Buchanan (1948) traced the sources of all nine atoms of purine ring1. In de novo synthesis, Inosine-5-P (Inosine Monophosphate, IMP) is the first nucleotide formed2. It is ,then, converted to

8、either AMP or GMP Location: liver cellular De novo purinenucleotide synthesis proceeds by the synthesis of the purine base upon the ribose sugar moietyN-1: aspartic acid C-2:THF - one carbon unitsN-3: glutamine C-4, C-5, N-7: glycine C-6: CO2 C-8: THF - one carbon unitsN-9: glutamineN-1C-2N-3C-6C-8N

9、-9H甘氨當(dāng)中站甘氨當(dāng)中站, , 谷氮坐兩邊谷氮坐兩邊, ,左上天冬氨左上天冬氨, , 頭頂頭頂COCO2 2二八倆一碳二八倆一碳N-7C-4C-51. First, synthesis Inosine-5-P (Inosine Monophosphate, IMP)R-5-PPRPP synthetasePP-1-R-5-P(PRPP)OHOOHPOOHHOHHOHHHOOHOOHPOOHHOHHOHHHOATP P_P5-5-磷酸核糖磷酸核糖胺胺,PRA ,PRA T T1/21/2 30s 30s甘氨酰胺甘氨酰胺核苷酸核苷酸(GAR)甲酰甲酰甘氨酰胺核苷酸甘氨酰胺核苷酸(FGAR)甲酰甘

10、氨甲酰甘氨咪咪核苷酸核苷酸(FGAM)5-氨基氨基咪唑咪唑核苷酸核苷酸(AIR)5-氨基咪唑-4-羧酸核苷酸5-氨基咪唑氨基咪唑-4-(N-琥珀酸琥珀酸)-甲酰胺甲酰胺核苷酸核苷酸(SAICAR)5-氨基咪唑氨基咪唑-4-(N-琥珀酸琥珀酸)-甲酰胺甲酰胺核苷酸核苷酸(SAICAR)5-氨基咪唑氨基咪唑-4-甲酰胺甲酰胺核苷酸核苷酸(AICAR)5-甲酰胺基咪唑甲酰胺基咪唑-4-甲酰胺甲酰胺核苷酸核苷酸(FAICAR)NH3 via glutamineNH3 via glutamine1 carbon via folate1 carbon via folateNH3 via aspartyl-

11、 succinate(2) ATP dependent stepATP dependent stepATP dependent stepATP dependent stepATP dependent stepPRPPInosine monophosphate2.Second, Making AMP and GMP kinaseADPkinaseADPATPATPADPAMPATPkinaseGDPkinaseADPGTPATPADPGMPATPRegulation of De Novo SynthesisATP provides the energy for GMP synthesisGTP

12、provides the energy for AMP synthesis3. “cross regulation” occurs from IMP to AMP and GMP2.End product inhibition and “feed forward” regulationCommitted Steps( at the first two steps ): PRPP , PRA(A bunch of steps you dont need to know)Purines are synthesized on the Ribose ringFeedbackInhibitionComm

13、itted Step8.1.2 Salvage Pathway for PurinesHypoxanthineorGuanine+ PRPP= IMP or GMP + PPi Hypoxanthineguanosylphosphoribosyl transferase(HGPRTase)Adenine+PRPP = AMP + PPi Adeninephosphoribosyl transferase(APRTase)Salvage pathways are particularly important in brain/marrow that lack de novo purine syn

14、thesisLesch-Nyhan Syndrome(萊萊- -尼綜合癥尼綜合癥)Absence of HGPRTaseX-linked (Gene on X)Occurs primarily in malesCharacterized by:purine synthesis is increased 200-foldIncreased uric acidSpasticity(痙攣)Neurological defectsAggressive behaviorSelf-mutilation(自殘)XMP AMPS AMPS（腺苷酸代琥珀酸）（腺苷酸代琥珀酸）IMPNH3Adenine Deam

15、inaseNADP+NH3NADPHGuanine ReductaseInter-conversion of Purine nucleotidesAMPGMPOHHHOHHHOCH2OHH1 2 3 4 5 BASEOHHHOHHHOCH2OHOH1 2 3 4 5 BASEDeoxyribonucleosideRibonucleosideRibonucleotideReductase8.1.3 Deoxyribonucleotide Biosynthesisribonucleotide reductaseADPdADPGDPdGDPribonucleotide reductaseUDPdUD

16、Pribonucleotide reductaseCDPdCDPribonucleotide reductaseTDPdTDP Deoxyribonucleotide Biosynthesis ?Mg2+硫氧還蛋白硫氧還蛋白 Ribonucleotides can be converted to deoxyribonucleotides by Ribonucleotide Reductase at the diphosphate levelThe ribonucleotide reductase, An (R1)2(R2)2- type enzyme , has R1 (86 kD) and

17、R2 (43.5 kD) two subunits E. coli Ribonucleotide Reductase Regulates the level of cellular dNTPskinasedCDP+ATPdCTP+ADPdUDP+ATPdUTP+ADPkinasedGDP+ATPdGTP+ADPkinasedADP+ATPdATP +ADPkinasedTTP?dNDPdNMP+PiphosphorylaseRegulation of dNTP Synthesis The overall activity of ribonucleotide reductase must be

18、regulated Balance of the four deoxynucleotides must be controlled ATP activates, dATP inhibits at the overall activity site ATP, dATP, dTTP and dGTP bind at the specificity site to regulate the selection of substrates and the products madeRegulation of dNTP Synthesis over-growth + Heterogeneity ( nu

19、cleotides + protein )Tumor How to inhibit the biosynthesis of the tumor cells?for anti-cancer strategies(antibacterial)Chemotherapeutic Agents1. Analogs of purine:8-氮雜鳥嘌呤氮雜鳥嘌呤N OHNNNHN SHNNNHN SHNNNHH2NN OHNNNHN6-巰基鳥嘌呤巰基鳥嘌呤inosine6-巰基嘌呤巰基嘌呤（6-mercaptopurine,6-MP）(8-azoguanine)(6-mercaptoguanine)2. A

20、nalogs of amino acids:H2NCCH2CH2CHCOOHONH2N+ NCH2COCH2CHCOOHONH2N+ NCH2CCH2CH2CHCOOHONH2Gln氮雜絲氨酸氮雜絲氨酸（azaserine）6-重氮重氮-5-氧正亮氨酸氧正亮氨酸(diazonnorleucine)Inhibit the reactions of the Gln3. Analogs of Folic acidR=H，aminopterin,氨喋呤氨喋呤R=CH3，methotrexate,氨甲喋呤氨甲喋呤,MTXN NH2NNNHH2NCH2NRCNCHOCH2CH2COOHCOOHHNNCHC

21、H2NHCNCHOCH2CH2COOHCOOHHH2NNOHNH四氫葉酸四氫葉酸,FH4PRPPGln6MP氮雜絲氨酸氮雜絲氨酸(azaserine)PRAGARFGARFGAMMTXazaserineAICARMTXFAICARIMPAMPGMPPRPPPPiPPiPRPP6MP6MP6MPazaserineAIGPRPPPPiThe mechanism of the Chemotherapeutic AgentsAMPIGMPGXXO XOExcreted inUrineSequential removal of bits and piecesEnd product is uric aci

22、dXO: Xanthine Oxidase 8.1.4 Purine The scale of uric acid (normal value) : 0.120.36mmol/L; male, 0.27mmol/L; formale, 0.21mmol/L0.48mmol/L(8mg%),Xanthine Oxidase and Gout別嘌呤醇別嘌呤醇次黃嘌呤次黃嘌呤 IAllopurinol, which inhibits XO, is a treatment of goutC OHNNNHHNN OHNNNHCHIallopurinolPRPPAllopurinol nucleotide

23、XOPurine nucleotidesThe mechanism of allopurinol as a treatment of goutUric acidsX8.2 Pyrimidine BiosynthesisPyrimidine Biosynthesis: In contrast to purines, First, synthesis of the pyrimidine ring; Next, attachment of ribose-phosphate to the ringCarbamoyl-PAspartate De Novo Pyrimidine BiosynthesisN

24、H2HCH2CHOOCHOOC乳清酸二氫乳清酸乳清酸核苷酸 CTP From UTP at the triphosphate levelUDPADPUTPATPADPUMPATPkinasekinase1. Thymine nucleotides are made from dUMP, which derives from dUDP, dCDP2. Biosynthesis of deoxyribonucleotides by ribonucleotide reductase3. Biosynthesis of thymidine monophosphate (dTMP) by thymidy

25、late synthaseSynthesis of Thymine NucleotidesCOHNCCHCHNOdR-5-PdUMPCOHNCC-CH3CHNOdR-5-PdTMP synthaseFH2N5,N10- methylene FH4FH4DHFRNADPH+H+NADP+dTMPkinasedTDPkinaseADPdTTPATPADPdTMPATPThymidylate synthase methylates dUMP at 5-position to make dTMPN5,N10-methylene THF is 1-C donorRegulation of Pyrimid

26、ine Synthesis（de novo） Aspartate transcarbamoylase (ATCase 細(xì)菌) catalyzes the condensation of carbamoyl phosphate with aspartate to form carbamoyl-aspartate Note that carbamoyl phosphate represents an activated carbamoyl group Feedback InhibitionRegulation of Pyrimidines BiosynthesisRegulation occurs

27、 at first step in the pathway (committed step)Inhibited by UTPIf you have lots of UTP around this means you wont make more that you dont need2ATP + CO2 + Glutamine = carbamoyl phosphateCPS II Carbamoyl phosphate for pyrimidine synthesis is made by carbamoyl phosphate synthetase II (CPS II 哺乳動(dòng)物細(xì)胞) Th

28、is is a cytosolic enzyme (whereas CPS I is mitochondrial and used for the urea cycle) Substrates are HCO3-, glutamine, 2 ATP Allosteric regulation of pyrimidine biosynthesis Enzyme regulatedAllosteric effector Effectcarbamoyl phosphate synthetase II UDP, UTPFeedback inhibition PRPP, ATPstimulatoryCP

29、S-I vs. CPS-II ?Biosynthesis: Purine vs. Pyrimidinestart with ribose, build on nitrogen baseRegulated by GTP/ATPGenerates IMPRequires Energybuild nitrogen base then added to PRPPSynthesized Regulated by UTPGenerates UMP/CMPRequires Energy“Both are very complicated multi-step process whichyour kindly

30、 professor does not expect you to know in detail”Salvaging Pyrimidines Pyrimidines+PRPP Nucleoside+PPi (嘧啶磷酸核糖轉(zhuǎn)移酶) A second type of salvage pathway involves two steps and is the major pathway for the pyrimidines, uracil and thymine Base + Ribose 1-phosphate = Nucleoside + Pi (nucleoside phosphorylas

31、e) Nucleoside + ATP Nucleotide + ADP (nucleoside kinase-irreversible) Analogs of pymidines /pymidine nucleosides:5-氟尿嘧啶5-Fu阿糖胞苷 Cytarabine 環(huán)胞苷Cyclocytidine NNHOOFHHOH2CHHHOOHHHOCCCNNCONH2HOH2CHHOHHHOCCCNNCNHHClOInhibitors of pymidines synthesis are cancer drugsUMPUDPUTPdUDPdUMPdTMPCTPCDPdCDPMTX5FU(5

32、FdUMP/5FUTP)阿糖胞苷Cytarabine氮雜絲氨酸 azaserineCONCCHCHNNH2HCOHNCCHCHNOHNH3COHNCCH2CH2NOHNADPH+H+NADP+H2OCOH2NCCH2CH2NOHHOH2OCO2+NH3H2N-CH2-CH2-COOH-AlanineCUPyrimidine Catabolism-1COHNCC-CH3CHNOHNADPH+H+NADP+COHNCCH-CH3CH2NOHCOH2NCCH-CH3CH2NOHHOH2OCO2+NH3-aminoisobutyrateH2N-CH2-CH-COOHCH3-脲基異丁酸脲基異丁酸H2OT

33、DHTPyrimidine Catabolism-2-氨基異丁酸氨基異丁酸overview5-P-RPRPPIMPdAMPGMPdGMPAMPdADPGDPdGDPADPdATPGTPdGTPATPUMPCMPdUMPUDPCDPdUDPUTPCTPdUTPdTMPdCMPdTDPdCDPdTTPdCTPCO2+GlnH2N-CO-POMPDe novo synthesisdUDPCPS-I vs. CPS-II氨基甲酰磷酸合成酶I氨基甲酰磷酸合成酶II分布線粒體(肝)胞液 氮源氨谷氨酰胺變構(gòu)激活劑N-乙酰谷氨酸無(wú)變構(gòu)抑制劑無(wú)UMP 功能尿素合成嘧啶合成(CPS-I)(CPS-II)選擇題練習(xí)

34、選擇題練習(xí)核苷酸代謝核苷酸代謝嘧啶核苷酸生物合成途徑的反饋抑制是由于控制了下列哪種酶的活性 ? A. 二氫乳清酸酶B. 乳清酸磷酸核糖轉(zhuǎn)移酶C. 二氫乳清酸脫氫酶D. 天冬氨酸轉(zhuǎn)氨甲酰酶E. 胸苷酸合成酶2. 5-氟尿嘧啶的抗癌作用機(jī)理是A. 合成錯(cuò)誤的DNAB. 抑制尿嘧啶的合成C. 抑制胞嘧啶的合成D. 抑制胸苷酸的合成E. 抑制二氫葉酸還原酶3. 哺乳類動(dòng)物體內(nèi)直接催化尿酸生成的酶是A. 尿酸氧化酶B. 黃嘌呤氧化酶C. 腺苷脫氨酸D. 鳥嘌呤脫氨酶E. 核苷酸酶4. 最能直接聯(lián)系核苷酸合成與糖代謝的物質(zhì)是A. 葡萄糖B. 6-磷酸葡萄糖C. 1-磷酸葡萄糖D. 1,6-二磷酸葡萄糖E. 5-磷酸核糖5. 體內(nèi)的脫氧核苷酸是由下列哪類物質(zhì)直接還原而成的A. 核糖B. 核糖核苷C. 一磷酸核苷D. 二磷酸核苷E. 三磷酸核苷6. 氮雜絲氨酸干擾核苷酸合成, 因?yàn)樗窍铝心?種化合物的類似物 ?A. 絲氨酸B. 甘氨酸C. 天冬氨酸D. 谷氨酰胺E. 天冬酰胺7. 能在體內(nèi)分解產(chǎn)生-氨基異丁酸的核苷酸是CMPAMPTMPUMPIMP關(guān)于天冬氨酸氨基甲?；D(zhuǎn)移酶的下列說(shuō)法, 哪一種是錯(cuò)誤的?GTP是其反饋抑制劑是嘧啶核苷酸從頭合成的調(diào)節(jié)酶是由多個(gè)亞基組成是變構(gòu)酶服