生物化学核酸的降解与核苷酸代谢课件.ppt

核酸的降解和核苷酸代谢,(Degradation of nucleic acid and nucleotides metabolism),一、核酸和核苷酸的分解代谢二、核苷酸的生物合成,核酸营养与核酸代谢,Nitrogenous Bases,Planar,aromatic,and heterocyclicDerived from purine or pyrimidine,Structure of Nucleotide Bases,Sugars,D-Ribose and 2-Deoxyribose,*Lacks a 2-OH group,Nucleosides,Result from linking one of the sugars with a purine or pyrimidine base through an N-glycosidic linkage Purines bond to the C1 carbon of the sugar at their N9 atoms Pyrimidines bond to the C1 carbon of the sugar at their N1 atoms,Phosphate Groups,Mono-,di-or triphosphates,Phosphates can be bonded to either C3 or C5 atoms of the sugar,Nucleotides,Result from linking one or more phosphates with a nucleoside onto the 5 end of the molecule through esterification,Nucleotides,DNA(deoxyribonucleic acid)is a polymer of deoxyribonucleotidesBoth deoxy-and ribonucleotides contain Adenine,Guanine and CytosineRibonucleotides contain UracilDeoxyribonucleotides contain Thymine,Monomers for nucleic acid polymersNucleoside Triphosphates are important energy carriers(ATP,GTP)Important components of coenzymes FAD,NAD+and Coenzyme A,FAD NAD,Coenzyme A：3-磷酸-ADP-泛酰-巯基乙胺,巯基乙胺,泛酸,ADP,Nucleosides:Purine nucleosides end in“-sine”Adenosine,GuanosinePyrimidine nucleosides end in“-dine”Thymidine,Cytidine,UridineNucleotides:Start with the nucleoside name from above and add“mono-”,“di-”,or“triphosphate”Adenosine Monophosphate,Cytidine Triphosphate,Deoxythymidine Diphosphate,1909-1934年，美国生物化学家Owen证明，核酸的分解单位是核苷酸。,1961年，美国生化学家Joan Oro模拟大气放电，在有氰化氢参加的反应体系中发现有氨基酸和腺嘌呤生成。,1963年，Ponnamperuma在类似的实验中也得到了腺嘌呤。后来，他又与Ruth Mariner、Carl Sagan将腺嘌呤与核糖连接成为腺苷；再连接磷酸，得到了腺苷三磷酸(ATP)。,核酸分解与合成背景知识,早在演绎核苷酸生物合成前，生物化学家就已经发现动物会排泄3种不同的含氮废物，即NH2、尿素和尿酸。尿酸就是嘌呤化合物的代谢产物。,在1950年间，John M.Buchanan和G.Robert Greenberg采用同位素示踪结合嘌呤核苷酸降解物尿酸分析证明，嘌呤分子的原子N1来自天冬氨酸，N3和N9来自谷氨酰胺等，完成了嘌呤生物合成过程的演绎。更为重要的是，他们还发现嘌呤不是以游离含氮碱，而是以核苷酸形式在体内合成的。,核酸分解与合成背景知识,1964年，科学家确定Lesch-Nyhan综合征与次黄嘌呤-鸟嘌呤磷酸核糖转移酶（HGPRT）缺陷有关。至今已发现，核苷酸的合成和分解代谢障碍与很多遗传性、代谢性疾病有关。模拟核苷酸组成成分，如取代碱基、核苷和核苷酸的类似物已发展为在临床上常用、有效的抗代谢药物。,核苷酸的功能,核苷酸是核酸生物合成的前体核苷酸衍生物是许多生物合成的活性中间物，例如：UDP-葡萄糖和CDP-二酯酰甘油分别是糖原和磷酸甘油酯合成的中间物ATP是生物能量代谢中通用的高能化合物腺苷酸是三种重要辅酶的组分某些核苷酸是代谢的调节物质。如：cAMP和cGMP是许多激素引起的胞内信使,1 核酸的酶促降解 核糖核酸酶、脱氧核糖核酸酶、限制性内切酶 2 核苷酸的降解 3 核苷酸的合成（1）核糖核苷酸的生物合成 嘌呤核苷酸的合成：从头合成和补救途径 嘧啶核苷酸的合成：从头合成和补救途径（2）脱氧核糖核苷酸的生物合成 核糖核苷酸的还原 脱氧胸腺嘧啶核苷酸的合成,核酸的降解和核苷酸代谢,第一部分核酸的解聚作用,动物和异养型微生物可以分泌消化酶来分解核蛋白和核酸类物质，以获得各种核苷酸。,（核苷水解酶主要存在于植物和微生物体内，并且只能对核糖核苷起作用，对脱氧核糖核苷不起作用。）,（核苷磷酸化酶存在广泛）,核酸的酶促降解,核酸的酶促降解,磷酸单酯酶,核糖,核酸,核酸酶,单核苷酸,核苷,嘧啶/嘌呤,核苷水解酶,核苷磷酸化酶,嘧啶（嘌呤）,核糖-1-磷酸,脱氧核糖-1-磷酸,核糖-5-磷酸,磷酸戊糖途径,醛缩酶,乙醛,甘油醛-3-磷酸,核 酸 酶,1、核酸酶的分类,（1）根据对底物的 专一性分为,（2）根据切割位点 分为,核酸外切酶：作用于核酸链的末端（3端或5端），逐个水解下核苷酸。脱氧核糖核酸外切酶：只作用DNA核糖核酸外切酶:只作用于RNA核酸内切酶：从核酸分子内部切断3,5-磷酸二酯键。限制性内切酶：在细菌细胞内存在的一类能识别并水解外源双链DNA的核酸内切酶，可用于特异切割DNA，常作为工具酶。,核酸酶：作用于核酸的磷酸二酯酶,外切核酸酶对核酸的水解位点,5,OH,B,3,B,B,B,B,B,B,B,牛脾磷酸二酯酶（5端外切得3核苷酸）,蛇毒磷酸二酯酶（3端外切得5核苷酸）,2、核酸酶的作用特点,限制性内切酶,类型 命名 意义,原核生物中存在着一类能识别外源DNA双螺旋中4-8个碱基对所组成的特异的具有二重旋转对称性的回文序列，并在此序列的某位点水解DNA双螺旋链的酶分子，产生粘性末端或平末端，这类酶称为限制性内切酶（restriction endonuclease）。,限制性内切酶名称的第一个字母取自获得此内切酶的细菌属名的第一个字母，用大写 名称的第二、三个字母取自该细菌种名的头二个字母，用小写字母 如果该细菌还有不同的株系，则另加第四个代表株系的字母或数字；最后是用罗马字大写的数字，代表同一菌株中不同限制性内切酶的编号。,限制性内切酶的命名和意义,例：Eco R I，这是从大肠杆菌（E.coli）R菌珠中分离出的一种限制性内切酶,如Hind 代表从流感噬血杆菌d株（Haemophilus influenzae）中分离到的第三种内切酶。,核苷酸的降解,核苷磷酸化酶普遍存在，催化反应是可逆的。核苷水解酶主要存在于植物与微生物中，并且只针对核糖核苷，对脱 氧核糖核苷是无作用的，反应是不可逆的。,第二部分碱基的分解代谢,嘌呤碱的分解Purine Catabolism,不同动物嘌呤代谢的产物 灵长类、鸟类：尿酸其他哺乳动物、软体动物：尿囊素 硬骨鱼：尿囊酸 软骨鱼和两栖类：尿素 大多数海洋无脊椎动物：氨和CO2（如甲壳类动物）All purine degradation leads to uric acid(but it might not stop there),嘌呤碱的分解首先是在各种脱氨酶的作用下水解脱去氨基。脱氨反应也可以在核苷或核苷酸的水平上进行，在动物组织中腺嘌呤脱氨酶的含量极少，而腺嘌呤核苷脱氨酶和腺嘌呤核苷酸脱氨酶的活性极高。,嘌呤碱的分解,嘌呤碱基的脱氨,嘌呤的降解,腺嘌呤 鸟嘌呤 H2O H2O NH3 NH3 次黄嘌呤 黄嘌呤 H2O+O2 H2O2 H2O+O2 H2O2 尿囊素 尿酸 H2O CO2+H2O2 2H2O+O2 尿囊酸 尿素+乙醛酸 H2O 4NH3+2CO2,腺嘌呤脱氨酶,鸟嘌呤脱氨酶,黄嘌呤氧化酶,黄嘌呤氧化酶,尿酸氧化酶,尿囊素酶,尿囊酸酶,脲酶,嘌呤的分解代谢,黄嘌呤氧化酶,尿酸的进一步分解,尿酸氧化酶,Adenosine Degradation,A CASE STUDY:GOUT,A 45-year-old man awoke from sleep with a painful and swollen right great toe.On the previous night he had eaten a meal of fried liver and onions,after which he met with his poker group and drank a number of beers.He saw his doctor that morning,“gouty arthritis”was diagnosed,and some tests were ordered.His serum uric acid level was elevated at 8.0 mg/L(NL7.0 mg/L).The man recalled that his father and his grandfather,both of whom were alcoholics,often complained of joint pain and swelling in their feet.,A CASE STUDY:GOUT,The doctor recommended that the man use NSAIDs for pain and swelling,increase his fluid intake(but not with alcohol)and rest and elevate his foot.He also prescribed allopurinol(别嘌呤醇).A few days later the condition had resolved and allopurinol had been stopped.A repeat uric acid level was obtained(7.1 mg/L).The doctor gave the man some advice regarding life style changes.,Gout,Impaired excretion or overproduction of uric acid 尿酸排泄的削弱与过量产生Uric acid crystals precipitate into joints(Gouty Arthritis),kidneys,ureters(stones)Xanthine oxidase（黄嘌呤氧化酶）inhibitors inhibit production of uric acid,and treat goutAllopurinol treatment hypoxanthine analog that binds to Xanthine Oxidase to decrease uric acid production,ALLOPURINOL IS A XANTHINE OXIDASE INHIBITORA SUBSTRATE ANALOG IS CONVERTED TO AN INHIBITOR,IN THIS CASE A“SUICIDE-INHIBITOR”,高嘌呤食物：豆苗、黄豆芽、芦笋、香菇、紫菜、动物内脏、鱼类,治疗痛风新药研发,饮酒与痛风,酒精在体内代谢产生乳酸，而血液乳酸水平的提高将抑制肾脏对尿酸的 排泄。啤酒中含有大量的嘌呤，饮酒相当于摄入了高嘌呤食物。饥饿状态下，体内代谢的调节可增加尿酸的形成进而影响尿酸的水平。,机 理：,治 疗：,采取有效的药物治疗合理控制饮食 多吃碱性食物和蔬菜 少喝啤酒 多饮水，少喝汤（汤里存在大量的嘌呤）规律而健康的生活习惯适当参加体育及户外运动,Adenosine Deaminase Deficiency,In purine degradation,adenosine inosineEnzyme is Adenosine Deaminase(ADA)ADA deficiency results in SCIDSevere Combined ImmunodeficiencySelectively kills lymphocytesBoth B-and T-cellsMediate much of immune response,腺苷脱氨酶缺乏症Adenosine deaminase deficiency(ADA)：一种严重的免疫缺陷症，腺苷脱氨酶的缺乏可使T淋巴细胞因代谢产物的累积而死亡，从而导致严重的联合性免疫缺陷症（SCID）。通常导致婴儿出生几个月后死亡。,嘧啶的分解代谢,胞嘧啶和尿嘧啶的分解代谢,胞嘧啶,尿嘧啶,二氢尿嘧啶,-脲基丙酸,-丙氨酸,胸腺嘧啶的分解代谢,-脲基异丁酸-氨基异丁酸,二氢胸腺嘧啶,胸腺嘧啶,胞嘧啶,NH3,尿嘧啶,二氢尿嘧啶,H2O,CO2+NH3,-丙氨酸,胸腺嘧啶,-脲基异丁酸,-氨基异丁酸,H2O,丙二酸单酰CoA,乙酰CoA,TCA,肝,尿素,甲基丙二酸单酰CoA,琥珀酰CoA,TCA,糖异生,胸腺嘧啶的分解代谢,甲基丙酰半醛,第三部分核苷酸的生物合成,嘌呤核糖核苷酸的生物合成,Bases/Nucleosides/Nucleotides,Base,Base+Sugar=Nucleoside,Base+Sugar+Phosphate=Nucleotide,Adenine,Deoxyadenosine,Deoxyadenosine 5-triphosphate(dATP),概述：从头合成基本途径 半合成（补救合成）,（CO2/NH3/AA/戊糖）核糖核苷酸,分解的现成嘌呤、嘧啶,ATP,核苷酸合成的两条途径,核糖、氨基酸、CO2、NH3,核糖核苷酸,脱氧核苷酸,辅酶,RNA,核苷,碱基,脱氧核苷,DNA,补救途径 从头合成,嘌呤核苷酸环上原子来源,嘌呤核糖核苷酸的合成,次黄嘌呤核苷酸的合成,各种嘌呤核苷酸的合成是先合成次黄嘌呤核苷酸，再转变成各种嘌呤核苷酸。此途径叫嘌呤核苷酸的从头合成途径（de novo synthesis pathway）。次黄嘌呤核苷酸的合成是在核糖上合成次黄嘌呤的，而不是先合成次黄嘌呤，再与核糖结合的。,嘌呤核苷酸的合成,嘌呤核苷酸的合成代谢,谷氨酰胺提供N9,甘氨酸提供C4，5和N7,嘌呤核苷酸的合成,嘌呤核苷酸的合成代谢,一碳单位提供C8,谷氨酰胺提供N3,N10-甲酰FH4,嘌呤核苷酸的合成代谢,CO2提供C6,天冬氨酸提供N1,一碳单位提供C2,嘌呤核苷酸的合成代谢,天冬氨酸提供C6上的氨基,谷氨酰胺提供C2上的氨基,ATP和GTP的合成,嘌呤核苷酸的合成代谢,核苷酸合成的补救途径,生物体内除了能以简单前体物质“从头合成”（de novo synthesis）核苷酸外，还能利用预先形成的碱基和核糖合成核苷酸。这个途径称为“补救途径”（salvage pathway）。,嘌呤核苷酸合成的补救途径,核苷磷酸化酶,腺苷激酶,磷酸核糖转移酶,磷酸核糖转移酶,只有腺苷激酶，其他核苷酸只能按以下反应产生。,（A）,（B）,嘌呤核苷酸的合成代谢,PRPP,补救途径,5磷酸核糖焦磷酸,腺嘌呤,腺嘌呤磷酸核糖转移酶,嘌呤核苷酸合成特点,先形成IMP(次黄嘌呤核苷酸)，然后在单磷酸的水平上转变成AMP、GMP。IMP合成从5-P-核糖开始的，在ATP参与下先形成PRPP(5-磷酸核糖焦磷酸)嘌呤的各个原子是在PRPP的C1上逐渐加上去的。由Asp、Gln、Gly、甲酸、CO2 提供N和C，合成时先形成右环，再形成左环。四氢叶酸（FH4）是一碳单位的载体,嘌呤核苷酸生物合成的调节,别构酶：受终产物抑制；,受终产物抑制,受终产物抑制,Nucleotide Metabolism,PURINE RIBONUCLEOTIDES:formed de novoi.e.,purines are not initially synthesized as free basesFirst purine derivative formed is Inosine Mono-phosphate(IMP)The purine base is hypoxanthineAMP and GMP are formed from IMP,De novo synthesis,5-磷酸核糖胺,PRA,甘氨酰胺核苷酸,甲酰甘氨酰胺核苷酸,甲酰甘氨咪核苷酸,5-氨基咪唑核苷酸,5-氨基-4-羧酸咪唑核苷酸,5-氨基咪唑-4-(N-琥珀酸)-氨甲酰核苷酸,5-氨基咪唑-4-氨甲酰核苷酸,5-甲酰胺-4-氨甲酰咪唑核苷酸,Synthesis of AMP and GMP,延胡索酸,kinase,ADP,kinase,ADP,ATP,ATP,ADP,AMP,ATP,kinase,GDP,kinase,ADP,GTP,ATP,ADP,GMP,ATP,Purine Salvage,Adenine phosphoribosyl transferase(APRT)Adenine+PRPP AMP+PPiHypoxanthine-Guanine phosphoribosyl transferase(HGPRT)Hypoxanthine+PRPP IMP+PPiGuanine+PRPP GMP+PPi(NOTE:THESE ARE ALL REVERSIBLE REACTIONS),Purine Nucleotide Synthesis at a Glance,ATP is involved in 6 stepsPRPP in the first step of Purine synthesis is also a precursor for Pyrimidine Synthesis,His and Trp synthesis,Regulatory Control of Purine Nucleotide Biosynthesis,GTP is involved in AMP synthesis and ATP is involved in GMP synthesis(reciprocal control of production)PRPP is a biosynthetically“central”molecule Rate of AMP production increases with increasing concentrations of GTP;rate of GMP production increases with increasing concentrations of ATP,Intracellular Purine Catabolism,Nucleotides broken into nucleosides by action of 5-nucleotidase(hydrolysis reactions)Purine nucleoside phosphorylase(PNP)Inosine HypoxanthineXanthosine XanthineGuanosine GuanineRibose-1-phosphate splits offCan be isomerized to ribose-5-phosphateAdenosine is deaminated to Inosine(ADA),Intracellular Purine Catabolism,Xanthine is the point of convergence for the metabolism of the purine basesXanthine Uric acidXanthine oxidase catalyzes two reactions,雷-纳（二氏）综合症 LeschNyhan syndrome,1964年首由Lesch和Nyhan二氏报道的一种先天性的代谢疾病。表现为血高尿酸症、高度智力障碍、脑源性麻痹、自伤症（自我咬伤）等的伴性遗传性疾病。发病的本质是基于组织中缺少与嘌呤有关的一种酶次黄嘌呤鸟嘌呤转磷酸核糖基酶（hypoxanthine（guanine）phosphoribosyltransferase，HGPRT），鸟嘌呤和次黄嘌呤补救途径障碍，导致产生过量的尿酸，导致肾结石和痛风。自我咬伤是咬自己的手指、嘴唇、颊部的一种怪癖，可作本症的一种重要特征。对于诊断原因不明的脑源性麻痹的男性病例中，在怀疑为本症时，测定其尿中和血中的尿酸是必要的。,Lesch-Nyhan Syndrome,A defect in production or activity of HGPRT Hypoxanthine-Guanine phosphoribosyl transferase Hypoxanthine+PRPP IMP+PPiCauses increased level of Hypoxanthine and Guanine(in degradation to uric acid)Causes gout-like symptoms,but also neurological symptoms spasticity,aggressiveness,self-mutilation 痉挛 具有侵略性 自我伤害First neuropsychiatric abnormality that was attributed to a single enzyme(神经精神不正常),嘧啶核糖核苷酸的生物合成,嘧啶核苷酸的嘧啶环是由氨甲酰磷酸和天冬氨酸合成的。,氨甲酰磷酸,天冬氨酸,嘧啶核苷酸的生物合成,嘧啶核苷酸合成特点：其合成与嘌呤核苷酸的合成不同，先由氨甲酰磷酸与天冬氨酸形成嘧啶环，再与5-磷酸核糖焦磷酸（PRPP）结合形成 UMP，其关键的中间产物是乳清酸。胞苷酸则由尿苷酸在三磷酸的水平上转变而来。,嘧啶环碳原子和氮原子的来源,嘧啶核苷酸的合成代谢,天冬氨酸,氨基甲酰磷酸的合成,CO2提供C2，Gln提供N3,嘧啶核苷酸的合成代谢,乳清酸的合成,嘧啶核苷酸的合成代谢,嘧啶核苷酸的合成代谢,嘧啶核苷酸的合成代谢,ATP提供能量,嘧啶核苷酸合成的补救途径,UMP磷酸核糖转移酶,尿苷磷酸化酶,尿苷激酶,胞苷激酶,胞嘧啶一般只参与嘧啶核苷激酶催化的这种途径,(A),(B),嘧啶核苷酸的合成代谢,Pyrimidine Ribonucleotide Synthesis,Uridine Monophosphate(UMP)is synthesized firstCTP is synthesized from UTPPyrimidine ring synthesis completed first;then attached to ribose-5-phosphate,N1,C4,C5,C6:AspartateC2:HCO3-N3:Glutamine amide Nitrogen,Pyrimidine Synthesis,UMP Synthesis Overview,2 ATPs needed:both used in first stepOne transfers phosphate,the other is hydrolyzed to ADP and Pi2 condensation:form carbamoyl aspartate and dihydroorotate(intramolecular)Attachment of base to ribose ring is catalyzed by OPRT;PRPP provides ribose-5-PPPi splits off PRPP irreversible,嘧啶核苷酸合成的调节,氨甲酰磷酸合成酶,天冬氨酸转氨甲酰酶,CTP合成酶,乳清酸尿症(Oroticaciduria),乳清酸尿症是一种遗传性疾病，主要表现为尿中排出大量乳清酸、生长迟缓和重度贫血。是由于催化嘧啶核苷酸从头合成反应(5)和(6)的双功能酶(乳清酸磷酸核糖转移酶（OPRT）和乳清酸脱羧酶（OMP脱羧酶）)的基因缺陷所致。临床用尿苷或胞苷治疗。尿苷经磷酸化可生成UMP，抑制CPS(氨基甲酰磷酸合成酶）活性，从而抑制嘧啶核苷酸的从头合成，从而避免乳清酸在体内的积累。,Orotic Aciduria,Caused by defect in protein chain with enzyme activities of last two steps of pyrimidine synthesisIncreased excretion of orotic acid in urine Symptoms:retarded growth;severe anemiaOnly known inherited defect in this pathway(all others would be lethal to fetus)Treat with uridine/cytidine,脱氧核糖核苷酸的生物合成,脱氧核糖核苷酸的合成,脱氧核糖核苷酸是由核糖核苷酸还原产生的。在生物体内，腺嘌呤、鸟嘌呤、胞嘧啶和尿嘧啶四种核糖核苷酸都可以被还原成相应的脱氧核糖核苷酸。催化此反应的酶称为核糖核苷酸还原酶。,大肠杆菌核糖核苷酸还原酶,核糖核苷酸还原酶由R1和R2两个亚基组成，它们分开时没有活性，只有合在一起并有镁离子存在时才有活性。R1亚基含有两条相同的多肽链，每条多肽链上有两个别构调节位点。一个调节位点结合效应物后影响对底物的特异性，另一个调节位点结合效应物后调节酶的活性，每条肽链上还含有一对参与催化氧化还原反应的巯基。每个R2亚基均含有参与催化氧化还原反应的酪氨酸。,核糖核苷酸还原酶示意图,底物特异性调节位点,酶活性调节位点,活性位点,R1亚基,R2亚基,一对巯基和一个酪氨酸,推进UDP和CDP的还原,推进GDP和ADP的还原,别构效应物,硫氧还蛋白,核糖核苷酸还原酶系,硫氧还蛋白还原酶,核糖核苷酸还原酶,核糖核苷酸的还原反应,核糖核苷酸还原酶,NADP+,NADPH+H+,硫氧还蛋白还原酶,FADH2,ATP、Mg2+,Formation of Deoxyribonucleotides,oxidized,reduced,核糖核苷酸还原酶催化反应时的氢传递过程,脱氧胸腺嘧啶核苷酸的合成,胸腺嘧啶核苷酸合成酶,NADPH+H+Ser,NADP+Gly,N5、N10CH2 FH4 FH2,二氢叶酸还原酶,Ser羟甲基转移酶,O,N,HN,O,dR-P,CH3,O,N,HN,O,dR-P,dUMP,dTMP synthase,FH2,N5,N10-methylene FH4,FH4,NADPH+H+,NADP+,dTMP,kinase,dTDP,kinase,ADP,dTTP,ATP,ADP,dTMP,ATP,Thymidylate synthase methylates dUMP at 5-position to make dTMP,N5,N10-methylene THF is 1-C donor,Synthesis of the Thymine Nucleotides,叶酸和四氢叶酸（FH4）,叶酸,N5，N10-CH2-FH4,核苷酸合成的其他反应,AMP激酶,核苷二磷酸激酶,脱氧核糖基转移酶,有4种针对不同NMP的激酶,此酶特异性不强,此酶可以使碱基与脱氧核苷上的碱基交换,嘌呤类似物（6-巯基嘌呤）：可抑制AMP、GMP的生成 谷胺酰胺类似物（氮杂丝氨酸）：可抑制IMP的合成中有谷胺酰胺参与的反应 叶酸类似物（氨基喋呤、氨甲喋呤）：可抑制IMP合成中有四氢叶酸参与的反应,临床上几种抗癌药物的作用机理,嘌呤核苷酸的抗代谢物,嘌呤类似物:,8-氮杂次黄嘌呤,H2N,6-巯基鸟嘌呤,次黄嘌呤,6-巯基嘌呤,（6-MP）,氨基酸类似物 抑制有谷氨酰胺参与的反应,谷氨酰胺,氮杂丝氨酸（重氮乙酰丝氨酸）,6-重氮-5-氧正亮氨酸,叶酸类似物 抑制有一碳单位参与的反应,R=H，氨基喋呤,R=CH3，氨甲喋呤,N,NH2,N,N,N,H,H2N,CH2N,R,CNCH,O,CH2,CH2,COOH,COOH,H,5,6,7,8四氢叶酸,核苷酸的抗代谢物,次黄嘌呤(H),6-巯基嘌呤(6-MP),MTX（氨甲喋呤）,MTX（氨甲喋呤）,Analogs of pymidines/pymidine nucleosides:,5-氟尿嘧啶5-Fu,阿糖胞苷 Cytarabine,环胞苷Cyclocytidine,Inhibitors of pymidines synthesis are cancer drugs,氮杂丝氨酸,阿糖胞苷,氨甲碟呤,氮杂丝氨酸,Deoxyribonucleotide Formation,Purine/Pyrimidine degradation are the same for ribonucleotides and deoxyribonucleotidesBiosynthetic pathways are only for ribonucleotide production Deoxyribonucleotides are synthesized from corresponding ribonucleotides,Formation of Deoxyribonucleotides,Reduction of 2 carbon done via a free radical mechanism catalyzed by“Ribonucleotide Reductases”E.coli RNR reduces ribonucleoside diphosphates(NDPs)to deoxyribonucleoside diphosphates(dNDPs)Two subunits:R1 and R2A Heterotetramer:(R1)2 and(R2)2 in vitro,RIBONUCLEOTIDE REDUCTASE,R1 SUBUNITTwo allosteric sitesSpecificity SiteActivity SiteFour redox-active SH groups from cysteinesR2 SUBUNITTyr 122 radicalBinuclear Fe(III)complex,The R2 dimer of ribonucleotide reductase,with a Tyr radical and a Fe3+-Fe3+binuclear center.,Tyr radical,Fe3+-Fe3+,Mechanism of Ribonucleotide Reductase Reaction,Free RadicalInvolvement of multiple SH groupsRR is left with a disulfide group that must be reduced to return to the original enzyme,Thioredoxin（硫氧还蛋白）,Physiologic reducing agentCys pair can swap H atoms with disulfide formed regenerate original enzymeThioredoxin gets oxidized to disulfide,Oxidized Thioredoxin gets reduced by thioredoxin reductase mediatedby NADPH(final electron acceptor),Thymine Formation,Formed by methylating deoxyuridine monophosphate(dUMP)UTP is needed for RNA production,but dUTP not needed for DNAIf dUTP produced excessively,would cause substitution errors(dUTP for dTTP)dUTP hydrolyzed by dUTPase(dUTP diphosphohydrolase)to dUMP methylated at C5 to form dTMPrephosphorylate to form dTTP,Tetrahydrofolate(THF),Methylation of dUMP catalyzed by thymidylate synthase Cofactor:N5,N10-methylene THF（甲叉四氢叶酸）oxidized to dihydrofolateTHF Regeneration:DHF+NADPH+H+THF+NADP+(enzyme:dihydrofolate reductase)THF+Serine N5,N10-methylene-THF+Glycine(enzyme:serine hydroxymethyl transferase),dUMP,dTMP,NADPH+H+,NADP+,SERINE,GLYCINE,REGENERATION OF N5,N10 METHYLENETETRAHYDROFOLATE,DHF,N5,N10 METHYLENE-THF,THF,dihydrofolate reductase,serine hydroxymethyl transferase,thymidylate synthase,Anti-Folate Drugs,Cancer cells consume dTMP quickly for DNA replicationInterfere with thymidylate synthase to decrease dTMP production(fluorodeoxyuridylate irreversible inhibitor)also affects rapidly growing normal cells(hair follicles,bone marrow,immune system,intestinal mucosa)Dihydrofolate reductase step can be stopped competitively(DHF analogs)Anti-Folates:Aminopterin（氨蝶呤）,methotrexate（甲氨蝶呤）,trimethoprim（甲氧苄啶）,本章小结,核苷酸分解代谢,嘌