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Nucleotide Metabolism2555

Chalermchai Mitrpant

OutlineOutline• Structure of nucleotide

• Biosynthesis of pyrimidine nucleotide

• Function of nucleotide

• Biosynthesis of purine nucleotide

De novo and Salvage pathway and its regulatory mechanism 

De novo and Salvage pathway and its regulatory mechanism 

• Diseases relating to nucleotide synthesis

• Biosynthesis of deoxynucleotide and its regulatory mechanism

• Catabolism of pyrimidine nucleotide and related diseases

• Catabolism of purine nucleotide and related diseases

• Biosynthesis of Coenzymes

• Medication related to nucleotide metabolism

Structure and function of NucleotideStructure and function of Nucleotide

Structure of NucleotideStructure of Nucleotide

Function of NucleotideFunction of Nucleotide

1. เปนหนวยยอย (monomeric unit) ใชในการสรางกรดนิวคลีอิคซึ่งในรางกายแบงไดเปน 2 พวก คือ DNA (deoxyribonucleic acid) และ RNA (ribonucleic acid)

2. Adenosine triphosphate (ATP); เปนสารใหพลังงานสงู มีความสําคัญ ในการขับเคลื่อนปฏิกิริยาตางๆที่จําเปนตองใชพลงังาน โดยปฏิกิริยาสลาย ATP (ATP hydrolysis) จะสงผานพลังงานเสรี เพื่อเปลี่ยนสมดุลของปฏิกิริยาใหัเกิดไดงายขึ้น (ATP coupling)

3. เปนสื่อกลาง (mediator) ของขบวนการตางๆในรางกาย เชน cyclic AMP (cAMP), cyclic GMP (cGMP)

4. เปนสารตนในการสังเคราะห cofactor บางชนิด เชน GTP ใชในการสังเคราะห tetrahydrobiopterin

5. เปนสวนประกอบของโคเอนไซม เชน NAD (nicotinamide adenine dinucleotide), FAD (flavin adenine dinucleotide) และ coenzyme A 

Function of NucleotideFunction of Nucleotide

6. ชวย นํา สาร intermediates ในปฏิกิริยาบางอยาง เชน UDP‐glucose (Glycogen synthesis), CDP‐choline, และ CDP‐diacylglycerol (glycolipid synthesis), 7‐methylguanosine triphosphate (RNA modification)

7. เปน allosteric effector ที่ควบคุมการทํางานของเอนไซมหลายชนิด

8. AMP ทําหนาที่ metabolic sensor ควบคุมเมแทบโบลิซึมในเซลล ทํางานสัมพันธกันกับ adenylate kinase (AK) และ AMP kinase (AMPK)

9. ADP ทําหนาที่เกี่ยวของกบัการเกาะกลุมของเกล็ดเลอืด ภายหลังจากเกล็ดเลอืดถูกกระตุน จะหลั่ง ADP และ ADP นี้เองจะจับกับ adenosine receptor P2Y12 บนผิวของเกลด็เลือดนํา ไปสูการเกาะกลุมของเกล็ดเลอืด 

AMP as a metabolic sensorAMP as a metabolic sensor

ADP

Clopidogrel

ADP as a mediator for platelet activationADP as a mediator for platelet activation

BiosynthesisBiosynthesis

Biosynthesis of nucleotideBiosynthesis of nucleotide

Purine nucleotide Pyrimidine nucleotide

• De no vo

• Salvage

• De no vo

• Salvage

Synthesis of PRPPSynthesis of PRPP

Voet Biochemistry 3e© 2004 John Wiley & Sons, Inc.

The metabolic pathway for the de novo The metabolic pathway for the de novo biosynthesis of IMPbiosynthesis of IMP

Voet Biochemistry 3e© 2004 John Wiley & Sons, Inc.

IMP is converted to AMP or GMP in IMP is converted to AMP or GMP in separate two reactionsseparate two reactions

Voet Biochemistry 3e© 2004 John Wiley & Sons, Inc.

The biosynthetic origins of purine ring atomsThe biosynthetic origins of purine ring atoms

IMP

De novo Purine synthesisDe novo Purine synthesis

Voet Biochemistry 3e© 2004 John Wiley & Sons, Inc.

IMP is converted to AMP or GMP in IMP is converted to AMP or GMP in separate two reactionsseparate two reactions

Regulation of de novo Purine synthesisRegulation of de novo Purine synthesis

Salvage purine synthesisSalvage purine synthesis

Salvage purine synthesisSalvage purine synthesis

De novo Pyrimidine synthesisDe novo Pyrimidine synthesis

Salvage pyrimidine synthesisSalvage pyrimidine synthesis

Biosynthesis of deoxynucleotideBiosynthesis of deoxynucleotide

Substrate for RNA synthesis

Deoxyadenosine triphosphate dATP

dGTP

dCTP

dTTP

Substrate for DNA synthesis

Biosynthesis of deoxynucleotideBiosynthesis of deoxynucleotide

Biosynthesis of deoxynucleotideBiosynthesis of deoxynucleotide

Substrate for RNA synthesis

Deoxyadenosine triphosphate dATP

dGTP

dCTP

dTTP

Substrate for DNA synthesis

dUTP

Biosynthesis of deoxynucleotideBiosynthesis of deoxynucleotide

Regulation of ribodinucleotide reductaseRegulation of ribodinucleotide reductase

Diseases related to biosynthesis of nucleotideDiseases related to biosynthesis of nucleotide

Purine Pyrimidine

1. Lesch nyhan syndrome 1. Orotic aciduria

2. Renal lithiasis (APRT deficiency)

Lesch Nyhan syndromeLesch Nyhan syndrome

• X-linked recessive inherited disorder • Neurological dysfunction

• Cognitive and behavioral disturbance; self-mutilation

• Uric acid overproduction

How does Lesch Nyhan syndrome causes hyperuricemia

• Excess of hypoxanthine and guanine

• Reduced IMP and GMP

• Excess of PRPP

Management• Symptomatic treatment; benzodiazepine (reduced anxiety)

• Medication to reduce uric acid; Allopurinol & Probenecid

• SAM supplement (still in clinical research)

Lesch Nyhan syndromeLesch Nyhan syndrome

Guanine Deaminase

How does Lesch Nyhan syndrome How does Lesch Nyhan syndrome causes hyperuricemiacauses hyperuricemia

How does Lesch Nyhan syndrome How does Lesch Nyhan syndrome causes hyperuricemiacauses hyperuricemia

Role of SAM supplement in Role of SAM supplement in patient with Lesch Nyhan syndromepatient with Lesch Nyhan syndrome

APRT deficiencyAPRT deficiency

Excess adenine

8-hydroxy adenine

2,8-dihydroxy adenine

Xanthine oxidase

Xanthine oxidase

• Renal lithiasis 

• Renal failure

Orotic aciduriaOrotic aciduria

• Orotate decarboxylase or Orotate Phosphoribosyltransferase

• Growth Retardation

• Megaloblastic anemia

Symptoms

Management

• Uridine supplement

• Autosomal recessive

CatabolismCatabolism

Catabolism of purine nucleotideCatabolism of purine nucleotide

Catabolism of purine nucleotideCatabolism of purine nucleotide

Diseases related to catabolism of purineDiseases related to catabolism of purine

2. Severe combined immune deficiency (Adenosine deaminase)

1 .Purine nucleotide phosphorylase

3. Gout

Purine nucleotide phosphorylase deficiencyPurine nucleotide phosphorylase deficiency

• Defect in T-lymphocyte related immunological defense(2/3 of cases)

• Excess 1,2 & 3 can be excreted by kidney

• Excess of 1. inosine, 2. deoxyinosine, 3. Guanosine and 4. deoxyguanosine

• Deoxyguanosine -------> dGTP

Purine nucleotide phosphorylase deficiencyPurine nucleotide phosphorylase deficiency

dGTP

Purine nucleotide phosphorylase deficiencyPurine nucleotide phosphorylase deficiency

dATP

Overall Inhibition of RNR

Inhibit DNA synthesis

Specific activation of RNR

Loss in mitochondrial membrane potential

Apoptosis of thymocyte in Thymus

Effect on number and function of T‐lymphocyte

Adenosine deaminase deficiencyAdenosine deaminase deficiency

• Defect in both T- and B-lymphocyte related immunological defense

• Excess deoxyadenosine -------> dATP

• Severe combined immunodeficiency (SCID)

• Inhibit RNR and inhibit Lymphocyte proliferation

Adenosine deaminase deficiencyAdenosine deaminase deficiency

Hyperuricemia and GoutHyperuricemia and Gout

• Uric; Final degradative product of purine in human

• Deposition of urate crystal causes Gout (Gouty arthritis)

• Not well-dissolved in water

• Increased purine synthesis

• Increased purine catabolism; patient with cancer prescribed on chemotherapy

• Genetic disease; Lesch Nyhan syndrome and PRPS hyperactivity

• Decreased Excretion

Cause of HyperuricemiaCause of Hyperuricemia

• Glucose-6-phosphatase deficiencyExcess G-6-P promotes Pentose phosphate pathway

• Polymorphism on urate transporter ATP binding G2 (ABCG2) decreases rate of urate transport and then decrease urate secretion

Catabolism of purine nucleotide Catabolism of purine nucleotide and uric acid excretionand uric acid excretion

Voet Biochemistry 3e© 2004 John Wiley & Sons, Inc.

Mechanism of competitive inhibitor of Allopurinol on xanthine oxidase

Catabolism of pyrimidine nucleotide Catabolism of pyrimidine nucleotide

1. 5’-Nucleotidase deficiency

2. Lead poisoning

Diseases related to catabolism of pyrimidineDiseases related to catabolism of pyrimidine

Disease relating to Catabolism of pyrimidineDisease relating to Catabolism of pyrimidine

5’‐Nucleotidase deficiency

Hemolytic anemia

Basophilic strippling

Nucleotidase

PNP

Increased  CMP and UMP

Features is similar to lead poisoning associated hemolytic anemia

How can lead inhibit 5’Nucleotidase?

Decreased 5’‐Nucleotidase activityIn patient with lead poisoning

55’’--Nucleotidase inhibition in Lead poisoning Nucleotidase inhibition in Lead poisoning

Medications related to nucleotide metabolismMedications related to nucleotide metabolismand coenzyme synthesisand coenzyme synthesis

Antitumour drug in clinical usedAntitumour drug in clinical used1. Antimetabolite

• 5 Fluorouracil (5‐FU)

• 6 Mercaptopurine (6‐MP)

• Inhibit Thymidylate synthase (dUMP dTMP)

2. Antifolate

• Metrothexate• Aminopterin

• Interfere on gene splicing

• DNA damage

• Inhibit Amidophosphoribosyl transferase

• Inhibit IMP dehydrogenase

• Inhibit Adenylosuccinate synthetase

Inhibit Thymidylate synthase (dUMP dTMP)

Tetrahydrofolate

Mechanism of action of Mechanism of action of Antimetabolite and antifolateAntimetabolite and antifolate

Mechanism of action of 6Mechanism of action of 6--MPMP

Antitumour drug in clinical usedAntitumour drug in clinical used3. Glutamine antagonist

• Inhibit reactions required glutamine

• IMP  GMP conversion

• UTP  CTP conversion

• PRPP synthesis and CPSII

Antiproliferation drugAntiproliferation drug

Hydroxyurea

Antiviral drugAntiviral drug

Acyclovir (Acycloguanosine)

• Active form “Acycloguanosine triphosphate”

• AcycloGTP is the specific substrate for HSV DNA polymerase causing DNA chain termination 

• Metabolised to AcycloGMP only by Thymidine kinase of HSV (herpes simplex virus)

• Treatment for Herpes Zoster

Antiviral drugAntiviral drug

AZT (Zidovudin)

• Active form “AZT triphosphate”

• Inhibitory effect of AZT triphosphate on HIV DNA polymerase is 100 fold more sensitive than human DNA polymerase

• Metabolised to AcycloGMP by Thymidine kinase of host cell

• Treatment for Human immune deficiency viral infection

Biosynthesis of Nicotinamide Biosynthesis of Nicotinamide adenine dinucleotideadenine dinucleotide

Biosynthesis of flavin adenine dinucleotideBiosynthesis of flavin adenine dinucleotide

Biosynthesis of Coenzyme ABiosynthesis of Coenzyme A