Nucleotide Metabolism 2556

Chalermchai Mitrpant

Outline • 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 Nucleotide

Structure of Nucleotide

Function of Nucleotide

1. เปนหนวยยอย (monomeric unit) ใชในการสรางกรดนวคลอคซงในรางกายแบงไดเปน 2 พวก คอ DNA (deoxyribonucleic acid) และ RNA (ribonucleic acid)

2. Adenosine triphosphate (ATP); เปนสารใหพลงงานสง มความส าคญ ในการขบเคลอนปฏกรยาตางๆทจ าเปนตองใชพลงงาน โดยปฏกรยาสลาย ATP (ATP hydrolysis) จะสงผานพลงงานเสร เพอเปลยนสมดลของปฏกรยาใหเกดไดงายขน (ATP coupling)

3. เปนสอกลาง (mediator) ของขบวนการตางๆในรางกาย เชน cyclic AMP (cAMP),

cyclic GMP (cGMP)

4. เปนสารตนในการสงเคราะห cofactor บางชนด เชน GTP ใชในการสงเคราะห

tetrahydrobiopterin

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

Function of Nucleotide

6. ชวย น า สาร intermediates ในปฏกรยาบางอยาง เชน UDP-glucose (Glycogen synthesis), CDP-choline, และ CDP-diacylglycerol

(glycolipid synthesis)

7. เปน allosteric effector ทควบคมการท างานของเอนไซมหลายชนด

8. AMP ท าหนาท metabolic sensor ควบคมเมแทบโบลซมในเซลล ท างานสมพนธกนกบ adenylate kinase (AK) และ AMP kinase (AMPK)

9. ADP ท าหนาทเกยวของกบการเกาะกลมของเกลดเลอด ภายหลงจากเกลดเลอดถกกระตน จะหลง ADP และ ADP นเองจะจบกบ adenosine receptor P2Y12 บนผวของเกลดเลอดน า ไปสการเกาะกลมของเกลดเลอด

AMP as a metabolic sensor

ADP as a mediator for platelet activation

ADP

Clopidogrel

Biosynthesis

Biosynthesis of nucleotide

Purine nucleotide Pyrimidine nucleotide

• De novo

• Salvage

• De novo

• Salvage

Synthesis of PRPP

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

The metabolic pathway for the de novo

biosynthesis of IMP

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

IMP is converted to AMP or GMP in

separate two reactions

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

The biosynthetic origins of purine ring atoms

IMP

De novo Purine synthesis

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

IMP is converted to AMP or GMP in

separate two reactions

Regulation of de novo Purine synthesis

Salvage purine synthesis

Salvage purine synthesis

De novo Pyrimidine synthesis

Salvage pyrimidine synthesis

Uracil

Uracil

Uridine

Uridine

Biosynthesis of deoxynucleotide

Substrate for RNA synthesis

Deoxyadenosine triphosphate dATP

dGTP

dCTP

dTTP

Substrate for DNA synthesis

Biosynthesis of deoxynucleotide

Biosynthesis of deoxynucleotide

Substrate for RNA synthesis

Deoxyadenosine triphosphate

dATP

dGTP

dCTP

dTTP

Substrate for DNA synthesis

dUTP

Biosynthesis of deoxynucleotide (dTTP)

1. From dCDP

2. From dUDP

1. 2.

Biosynthesis of deoxynucleotide (dTTP)

Regulation of deoxynucleotide biosynthesis

Diseases related to biosynthesis of nucleotide

Purine Pyrimidine

1. Lesch nyhan syndrome 1. Orotic aciduria

2. Renal lithiasis

(APRT deficiency)

Lesch 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

Management

• Symptomatic treatment; benzodiazepine (reduced anxiety)

• Medication to reduce uric acid; Allopurinol & Probenecid

• SAM supplement (still in clinical research)

Lesch Nyhan syndrome

Guanine Deaminase

How does Lesch Nyhan syndrome

causes hyperuricemia

(Guanase)

How does Lesch Nyhan syndrome

causes hyperuricemia

Role of SAM supplement in

patient with Lesch Nyhan syndrome

APRT deficiency

Excess adenine

8-hydroxy adenine

2,8-dihydroxy adenine

Xanthine oxidase

Xanthine oxidase

• Renal lithiasis

• Renal failure

Orotic aciduria

• Orotate decarboxylase

or Orotate Phosphoribosyltransferase

• Growth Retardation

• Megaloblastic anemia

Symptoms

Management

• Uridine supplement

• Autosomal recessive

Uridine

Catabolism

Catabolism of purine nucleotide

Catabolism of purine nucleotide

Diseases related to catabolism of purine

2. Severe combined immune deficiency (Adenosine

deaminase)

1 .Purine nucleotide phosphorylase

3. Gout

Purine 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 deficiency

PNP

dGTP

Purine 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 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 deficiency

Overall Inhibition of RNR Inhibit DNA synthesis

Hyperuricemia 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 Hyperuricemia

• Glucose-6-phosphatase deficiency

Excess 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

and uric acid excretion

Probenecid

Allopurinol

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

Mechanism of competitive inhibitor of Allopurinol on xanthine oxidase

Catabolism of pyrimidine nucleotide

Nucleotidase

Nucleotidase

Nucleotidase

1. 5’-Nucleotidase deficiency

2. Lead poisoning

Diseases related to catabolism of pyrimidine

Disease relating to Catabolism of pyrimidine

5’-Nucleotidase deficiency

• Hemolytic anemia

• Basophilic strippling

Nucleotidase

PNP

• Increased CMP and UMP

Blood smear is similar to lead poisoning associated hemolytic anemia

How can lead inhibit 5’Nucleotidase?

Decreased 5’-Nucleotidase activity in patient with lead poisoning

5’-Nucleotidase inhibition in Lead poisoning

Medications related to nucleotide metabolism

and coenzyme synthesis

Antitumour drug in clinical used

1. Antimetabolite

• 5 Fluorouracil (5-FU)

• 6 Mercaptopurine (6-MP)

• Inhibit Thymidylate synthase (dUMPdTMP)

2. Antifolate

• Metrothexate

• Aminopterin

• Interfere on gene splicing

• DNA damage

• Inhibit Amidophosphoribosyl transferase

• Inhibit IMP dehydrogenase

• Inhibit Adenylosuccinate synthetase

Inhibit Thymidylate synthase (dUMPdTMP)

Tetrahydrofolate

Mechanism of action of

Antimetabolite and antifolate

Mechanism of action of 6-MP

Antitumour drug in clinical used

3. Glutamine antagonist

• Inhibit reactions required glutamine

IMP GMP conversion

UTP CTP conversion

PRPP synthesis and CPSII

Antiproliferation drug

Hydroxyurea

Antiviral 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 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 AZT-triphosphate by Thymidine kinase of host cell

• Treatment for Human immune deficiency viral infection

Biosynthesis of Nicotinamide adenine

dinucleotide

Biosynthesis of flavin adenine dinucleotide

Biosynthesis of Coenzyme A

1. หลงปรบเพมขนาด ตวอกษรบน slide ยงคงมขนาดเลก

2. มองไมเหนความเชอมโยงระหวางเนอหา ของ lecture แตละสวน

3. อาจารยบรรยายเรว ไมสามารถท าความเขาใจเนอหาไดทน

4. อาจารย บรรยายโดยไมชประเดนเนนจดส าคญของเนอหา

Response 2555