Nucleotide Metabolism

1. Nucleic acid metabolism Nucleotide Metabolism DNA metabolism RNA metabolism

2. 核酸代谢 主要内容: 核酸的降解及代谢 DNA的复制与修复 RNA的生物合成

3. Cellular Roles of Nucleotides • Energy metabolism (ATP)* • Monomeric units of nucleic acids* • Regulation of physiological processes • Adenosine controls coronary 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 and others

4. How I hope to make this at least bearable if not mildly interesting • Purines and Pyrimidines • Synthesis (de novo and salvage pathways) • Degradation • Relevant disease states • Relevant clinical applications You are not responsible for any structures

5. Two Purines Adenine Guanine Two Pyrimidines Thymine/Uracil Cytosine Purines and Pyrimidines

6. Nucleotide Metabolism Nucleotide degradation Nucleotide synthesis

7. Nucleotide degradation Purine Degradation Pyrimidine Degradation

8. 核苷酸酶核苷酸磷酸化酶 核苷酸 核苷 碱基+（脱氧）戊糖 磷酸 核苷酸酶（磷酸单酯酶） • 专一性的磷酸单酯酶: 3ˊ-核苷酸酶, 5ˊ-核苷酸酶 • 非专一性磷酸单酯酶

9. 核苷磷酸化酶 核苷 + Pi 碱基 + 核糖-1-P 核苷水解酶 核苷 + H2O 碱基+核糖 • 磷酸解 • 水解

10. Purine Degradation Other species further metabolize uric acid • Sequential removal of bits and pieces • End product is uric acid • Uric acid is primate-specific 灵长类的动物 Excreted in Urine Xanthine Oxidase Xanthine Uric Acid (黄嘌呤) (尿酸)

11. Pyrimidine Degradation • Pyrimindine rings can be fully degraded to soluble structures (Compare to purines that make uric acid) Degradation pathways are quite distinct for purines and pyrimidines, but salvage pathways are quite similar

12. Purine Degradation Other species further metabolize uric acid • Sequential removal of bits and pieces • End product is uric acid • Uric acid is primate-specific 灵长类的动物 Excreted in Urine Xanthine Oxidase Xanthine Uric Acid

13. 嘌呤的分解代谢: 不同种类的生物分解嘌呤的能力不同，产物也不同。人、灵长类、鸟类、某些爬虫类将嘌呤分解成尿酸，其他生物还可将尿酸进一步分解成尿囊素、尿囊酸、尿素、甚至CO2、NH3。

14. 核酸中的嘌呤主要是Ade、Gua首先脱氨，分别生成次黄嘌呤和黄嘌呤，再进一步代谢生成尿酸。核酸中的嘌呤主要是Ade、Gua首先脱氨，分别生成次黄嘌呤和黄嘌呤，再进一步代谢生成尿酸。

15. 尿酸 尿囊素 尿囊酸 Inosine: 次黄嘌呤核苷 Hypoxanthine: 次黄嘌呤 Xanthine: 黄嘌呤 Uric acid: 尿酸 Allantoin: 尿囊素 Allantoic acid: 尿囊酸

16. Inosine: 次黄嘌呤核苷 Hypoxanthine: 次黄嘌呤 Xanthine:黄嘌呤 Uric acid:尿酸

17. 灵长类 鸟类 爬行类 昆虫类 软骨鱼 两栖动物 其它孵乳类 硬骨鱼类 Uric acid: 尿酸； Allantoin: 尿囊素； Allantoic acid: 尿囊酸 Uric acid: 尿酸； Allantoin: 尿囊素； Allantoic acid: 尿囊酸

18. Purine catabolism in animals

19. X Allopurinol Avoid: Offal foods such as liver, kidneys, tripe, sweetbreads and tongue Excess Uric Acid Causes Gout （痛风） • Primary gout (hyperuricemia，高尿酸血症) • Inborn errors of metabolism that lead to overproduction of Uric Acid • Overactive de novo synthesis pathway • Leads to deposits of Uric Acid in the joints • Causes acute arthritic joint inflammation Xanthine Oxidase Xanthine Uric Acid (别嘌呤醇)

20. 尿酸过多导致痛风（gout）

21. 结构与次黄嘌呤很相似的别嘌呤醇（allopurinol）对黄嘌呤氧化酶有很强的抑制作用，可用来治疗痛风。结构与次黄嘌呤很相似的别嘌呤醇（allopurinol）对黄嘌呤氧化酶有很强的抑制作用，可用来治疗痛风。

22. 别嘌呤醇

23. IMP: 次黄嘌呤苷一磷酸 HGPRT: 次黄嘌呤苷鸟嘌呤磷酸核糖转移酶

24. 别嘌呤醇

25. Immunodeficiency Diseases Associated with Purine Degradation • Defect in adenosine deaminase • Removes amine from adenosine • SCID- severe combined immunodeficiency • “Bubble Boy” Disease • Defect in both B-cells and T-cells (Disease of Lymphocytes) • Patients extremely susceptible to infection - hence the Bubble Lymphocyte

26. Therapies for SCID • Can be diagnosed in infants through a simple blood test (white cell count) • Bone marrow transplant for infants • Familial donor • Continued administration of adenosine deaminase (ADA-PEG) • Gene therapy- repair defective gene in T-cells or blood stem cells

27. Pyrimidine Degradation • Pyrimindine rings can be fully degraded to soluble structures (Compare to purines that make uric acid) Degradation pathways are quite distinct for purines and pyrimidines, but salvage pathways are quite similar

28. 嘧啶碱的分解代谢 RNA：Cyt、Ura

29. DNA：Thy

30. 二氢尿嘧啶脱氢酶　 二氢嘧啶酶　 β-脲基丙酸酶 甲基丙二酸半醛

31. 二氢尿嘧啶脱氢酶　 (二氢胸腺嘧啶)

32. 二氢嘧啶酶　 (β- 脲基异丁酸)

33. (β- 脲基异丁酸) β-脲基丙酸酶 (β- 氨基异丁酸)

34. (β- 氨基异丁酸) (甲基丙二酸半醛)

35. Antimetabolites • Often drugs that inhibit cell growth are used to combat cancer. Many of these compounds are analogues of purine and pyrimidine bases or nucleotides. Many of these drugs must be activated by cellular enzymes. They affect nucleic acid synthesis and tumor cells tend to be more susceptible since they are dividing more rapidly

36. 6-Mercaptopurine (6-MP) • Purine Analogue • Used clinically to combat childhood leukemia Since 1963 cure rate has increased from ~4% to greater than 80% Inhibitor of Committed Step in de novo Purine Biosynthesis 6-mercaptopurine ribonucleotide PRPP + 6-MP This reaction is more active in tumor cells

37. Cytosine Arabinose (araC) • Metabolized to cytosine arabinose 5’-triphosphate (araCTP) • Analogue of CTP • Incorporated into DNA and inhibits chain synthesis • Used extensively for acute leukemias Cytosine Ribose Cytosine Arabinose Differs only in the sugar

39. AZT as an Anti-HIV Agent • 3’-Azido-2’-deoxythymidine • Pyrimidine Analogue • HIV is a retrovirus • RNA genome that is reverse-transcribed to DNA Viral polymerase is inhibited by AZT AZT AZT： 3’-叠氮-2’-脱氧胸腺嘧啶核苷 DNA RNA Protein

40. X Dihydrofolate Reductase Antifolates • Antifolates interfere with formation of dihydrofolate which is required for: • dTMP synthesis • de novo purine biosynthesis Thymidylate Synthase dUMP dTMP Dihydrofolate N5,N10-Methylene tetrahydrofolate Tetrahydrofolate

41. Antifolate Agents Mimic Folate

42. Hydroxyurea • Specifically inhibits ribonucleotide reductase NDP dNDP • Inhibits DNA synthesis without affecting RNA synthesis or other nucleotide pools Cleared from the body rapidly so not used extensively in the clinic

43. The BIG Picture • GMP, AMP, UMP on….. • Generation of dTMP • Common features of clinically relevant antimetabolites/antifolates Antiviral agents- how are they specific for the virally infected cells?

45. Nucleotide Metabolism Nucleotide synthesis

46. Synthesis Pathways • For both purines and pyrimidines there are two means of synthesis (often regulate one another) • de novo (from bits and parts) • salvage (recycle from pre-existing nucleotides) Salvage Pathway

47. 5’ Many Steps Require an Activated Ribose Sugar (PRPP)

48. X de novo Synthesis • Committed step: This is the point of no return • Occurs early in the biosynthetic pathway • Often regulated by final product (feedback inhibition)

49. Purine Biosynthesis (de novo) 6 1 5 7 8 2 4 9 3

50. X Inhibited by AMP, GMP, IMP Purine Biosynthesis (de novo) • Atoms derived from: • Aspartic acid • Glycine • Glutamine • CO2 • Tetrahydrofolate • Also requires • 4 ATP’s Committed Step Purines are synthesized on the Ribose ring