![NAD⁺ AND NADP⁺ PARTICIPATES IN DIFFERENT
METABOLIC REACTIONS
• NAD⁺ and NADP⁺ play distinctly different metabolic
reactions.
• Transfer of electrons from various substrates to NAD⁺
is facilitated in many tissue due to ↑[NAD⁺/NADH]
conc. ratio in their cells→ transfer of these reducing
equivalents to mitochondrial ETC→ production of
energy.
• On the contrary, transfer of electrons from NADPH to
lipogenic and steroidogenic tissue having
↑[NADPH/NADP⁺] conc. ratio →Reductive
biosynthesis.
• Most oxidative tissue involved in catabolic reactions
have ↑NAD⁺ and ↓NADH while tissues or organs
involved in anabolic reactions (reductive biosynthesis)
have ↓NADP⁺ and ↑NADPH.](https://image.slidesharecdn.com/nucleotidecoenzymesnaba-171105134551/85/BIOSYNTHESIS-OF-NUCLEOTIDE-COENZYMES-AND-THEIR-ROLE-IN-METABOLISM-12-320.jpg)
BIOSYNTHESIS OF NUCLEOTIDE COENZYMES AND THEIR ROLE IN METABOLISM
- 1. A DISCUSSION ON BIOSYNTHESIS OF NUCLEOTIDE CO-ENZYMES AND THEIR ROLE IN METABOLISM MODERATOR-DR. M. B. BORA PRESENTER-DR. NABA References- 1. Harper,29th Ed 2. Biochemistry By D.Das,14th Ed. 3. Lehninger Principle Of Biochemistry,5th Ed. 4. Lubert Stryer,6th Ed. 5. D.Voet & I.G.Voet,4th Ed. 6. Internet
- 2. NUCLEOTIDES ARE THE BUILDING BLOCKS OF AMINO ACID WHICH CONSISTS OF- -NITOGENOUS BASE NUCLEOSIDE -PENTOSE SUGAR NUCLEOTIDE -PHOSPHATE PHOSPHATE Nitrogen containing base Pentose sugar Phosphate
- 3. What are nucleotide coenzymes? • A nucleotide coenzyme is a compound including in its structure at least one simple nucleotide moiety. • Nucleotide coenzymes function in association with specific proteins or apoenzymes. • Historically, the first nucleotide coenzyme discovered was cozymase, or diphosphopyridine nucleotide.
- 4. GLIMPSE INTO THE HISTORY The coenzyme NAD+ was first discovered by British biochemists Arthur Harden and William John Young in 1904. They noticed that yeast extract lost it’s ability to ferment glucose to ethyl alcohol when the extract was dialysed. They called the unidentified factor responsible for this effect a coferment . This heat-stable factor was identified as a nucleotide sugar phosphate by Hans von Euler-Chelpin(NP-1929). In 1936, the German scientist, Dr. Otto Heinrich Warburg(NP-1931) showed the function of the nucleotide coenzyme in hydride transfer and identified the nicotinamide portion as the site of redox reactions.
- 6. NAD⁺ BIOSYNTHESIS Nicotinamide moiety is derived in human from- Dietary Nicotinamide Nicotinic acid or Tryptophan. • Nicotinate phosphoribosyl transferase catalyzes the formation of nicotinate mononucleotide from nicotinate and PRPP. • Nicotinate mononucleotide may also be formed from ‘Quinolinate’, a degradation product of tryptophan, catalysed by quinolinate phosphoribosyl transferase (Liver and kidney). • Nicotinate mononucleotide is joined to ATP-derived AMP- residue by pyrophosphate linkage to form nicotinate adenine dinucleotide (desamido NAD+) catalyzed by NAD+ pyrophosphorylase. • NAD synthetase then convert intermediate to NAD+ by transamidation reaction where glutamine is the NH₂ donor.
- 7. NADP BIOSYNTHESIS • Nicotinamide moiety, derived from dietary nicotinamide is joined with phosphoribosyl-residue from PRPP to form nicotinamide mononucleotide catalyzed by nicotinamide phosphoribosyl transferase. • It is then joined with AMP-residue, derived from ATP by pyrophosphate linkage to form NAD⁺(Nicotinamide adenine dinucletide). • Finally, NADP is formed from ATP-dependent phosphorylation of c₂′-OH of adenine residue by NAD⁺kinase.
- 8. FORMATION OF NAD⁺ AND NADP⁺ FROM TRYPTOPHAN
- 10. BINDING OF NAD⁺ AND NADP WITH PROTEIN • Function as co-enzymes of pyridine dependent dehydrogenases. • Binds to a specific domain called ‘ROSSMANN’S FOLD’ (Michael Rossmann)by ionic & hydrogen bond. • This domain is formed of supersecondary motif consists of hexaparallel β- pleated sheath and four parallel α-helices in β-α-β-α-β arrangements. • Association is transient and loose.
- 11. NAD⁺/NADPH IN OXIDATION AND REDUCTION REACTIONS • It undergoes reversible reduction of nicotinamide ring (benzenoid form)(260nm) by accepting a hydride ion(:H ̄ )and get itself reduced to NADH/NADPH (quinonoid form)(340nm)releasing second proton to the aqueous medium. • Since association is loose and transient, nucleotide of both coenzymes move readily from one enzyme to another as water soluble electron carrier.
- 12. NAD⁺ AND NADP⁺ PARTICIPATES IN DIFFERENT METABOLIC REACTIONS • NAD⁺ and NADP⁺ play distinctly different metabolic reactions. • Transfer of electrons from various substrates to NAD⁺ is facilitated in many tissue due to ↑[NAD⁺/NADH] conc. ratio in their cells→ transfer of these reducing equivalents to mitochondrial ETC→ production of energy. • On the contrary, transfer of electrons from NADPH to lipogenic and steroidogenic tissue having ↑[NADPH/NADP⁺] conc. ratio →Reductive biosynthesis. • Most oxidative tissue involved in catabolic reactions have ↑NAD⁺ and ↓NADH while tissues or organs involved in anabolic reactions (reductive biosynthesis) have ↓NADP⁺ and ↑NADPH.
- 13. ENZYMES USING NAD⁺/NADH There are about 200 different types of enzymes using NAD⁺/NADH as their co-enzymes. Some important enzymes are- GLYCOLYSIS Glyceraldehyde 3-P Dehydrogenase Lactate dehydrogenase Pyruvate dehydrogenase complex (PDH)
- 14. ENZYMES USING NAD⁺/ NADH KREB’S CYCLE/TCA CYCLE- α-ketoglutarate Dehydrogenase Malate Dehydrogenase Isocitrate Dehydrogenase( Mitochondria) POLYOL PATHWAY- Sorbitol dehydrogenase
- 15. ENZYMES USING NAD⁺/NADH URONIC ACID PATHWAY- UDP-glucose dehydrogenase & Xylulose reductase ALCOHOL METABOLISM- Alcohol dehydrogenase & Aldehyde dehydrogenase β-OXIDATION OF FATTY ACID- β-hydroxyacyl co-A dehydrogenase OMEGA OXIDATION- Alcohol& Aldehyde Dehydrogenase CYSTINE REDUCTASE-Formation of L-cystine to L-cysteine.
- 20. SOME NON REDOX ROLE OF NAD⁺ • NAD is the source of ADP-ribose for ADP- ribosylation of proteins. • Cyclic ADP-ribose and nicotinic acid adenine dinucleotide, formed from NAD act to increase intracellular calcium in response to neurotransmitters and hormones. • BACTERIAL DNA LIGASE- uses NAD⁺ to donate AMP to 5′ end of one nucleotide to which another nucleotide add to it’s 3′ end to form phosphodiester bond. • SIRTUINS- NAD dependent deacetylase, related to aging is a topic of extensive research.
- 21. DRUGS AND DISEASES ASSOCIATED WITH NAD • ISONIAZID- React with NADH to inhibit Dihydro folate reductase(DHFR) and enoyl acyl carrier protein reductase. • MYCOPHENOLIC ACID AND TIAZOFURIN inhibit IMP dehydrogenase. • PALLEGRA- Due to deficiency of niacin or tryptophan. • Symptoms(3D)→Death (4D) • Diarrhoea- • Dementia- Tissue with high respiration rate such as CNS is severely effected. • Dermatitis-Due to ↑kynurenine/↓repair of UV induced damage to epidermis. • Potential role of NAD in therapy of patients suffering from neurodegenerative diseases like Alzheimer’s disease, parkinson’s disease is being studied.
- 22. FORMATION OF FMN AND FAD • Formed from riboflavin in liver, intestinal mucosa and other tissues. • 5′-OH group of ribityl side chain of riboflavin is phosphorylated by FLAVOKINASE and ATP forming FMN. • Then coupling of FMN and ATP-derived AMP(adenylate) occures by pyrophosphate linkage catalysed by FAD pyrophosphorylase to form FAD. • FMN is not a true nucleotide since it’s ribityl residue is not a true sugar.
- 23. SCHEMATIC DIAGRAM OF FORMATION OF FMN AND FAD
- 24. FLAVOPROTEIN IN OXIDATION AND REDUCTION • FLAVOPROTEIN-Enzymes catalyzing oxidation and reduction reactions using FMN or FAD as coenzymes (QUINONE). • SEMIQUINONE-When one pair of reducing equivalents are transferred from substrate to N¹ of isoalloxazine ring forming FMNH•/FADH•(450 nm). • HYDROQUINONE-Two pair of reducing equivalents are transferred to N¹ and N¹⁰ producing FMNH₂/FADH₂(360nm).
- 25. CHARACTERISTICS OF FLAVOPROTEIN • Flavin nucleotide in most flavoproteins are bound rather tightly to the protein. ex-succinate dehydrogenase- FAD is bound covalently like the prosthetic groups. • Cannot transfer electrons by diffusing from one enzyme to another, rather it can temporarily hold electrons and transfer it to an electron acceptor. • Tight association confers on the flavin ring a reduction potential(E⁰),different from reduction potential of free flavin nucleotide. • CRYPTOCHROMES- A family of flavoproteins, mediate the effect of blue light on plant development. • PHOTOLYASES-Found in bacteria & eukaryotes, uses energy of absorbed light to repair chemical defect in DNA. • METALLOFLAVOPROTEIN-Contain electron transferring metals like Fe and Mo in addition to FAD, FMN.eg- Xanthine oxidase & NADH dehydrogenase • HEMOFLAVOPROTEIN-Contain both heme and flavin.eg-L-lactate dehydrogenase of yeast.
- 26. FLAVOPROTEIN OXIDOREDUCTASE ENZYMES CONTAINING FAD • Succinate dehydrogenase • Acyl-coA dehydrogenase • Pyruvate dehydrogenase • α-ketoglutarate dehydrogenase • Choline dehydrogenase • D-amino acid oxidase • Xanthine oxidase • NADPH-cytochrome P 450 reductase • Glutathione reductase • α-glycerophosphate dehydrogenase(mitochondrial) ENZYMES CONTAINING FMN • NADH dehydrogenase • Cytochrome b₂ • L-amino acid oxidase • Glycolate oxidase
- 27. ENZYMES USING FAD • β-OXIDATION- Acyl co-A dehydrogenase • TCA CYCLE- Succinate dehydrogenase • PYRUVATE DEHYDROGENASE COMPLEX
- 28. ENZYMES USING FAD • Thioredoxin reductase • Choline dehydrogenase • D-amino acid oxidase H₂O₂ H₂0 2Fd red 2Fd ox BA DEHYDROGENASE CHOLINE → BETAINE ALDEHYDE → BETAINE NAD⁺ NADH+H⁺
- 29. ENZYMES USING FAD • Xanthine oxidase • GLYCEROPHOSPHATE SHUTTLE- α-glycerophosphate dehydrogenase (mitochondrial)
- 30. ENZYME USING FMN • L-amino acid oxidase • NADH dehydrogenase • Glycolate oxidase
- 31. ROLE OF NAD⁺/FAD IN ETC FLOW OF ELECTRONS THROUGH VARIOUS COMPLEXES
- 32. FORMATION OF COENZYME-A FROM PANTOTHENATE • Pantothenate at first is phosphorylated by pantothenate kinase to form 4- phosphopantothenate. • It is then coupled to cysteine catalysed by phosphopantothenoylcysteine synthetase to form 4- phosphopantothenoylcysteine. • It undergoes decarboxylation to form 4-phosphopantethiene. • It is then coupled to AMP by pyrophosphate linkage to form dephospho-coA by pyrophosphorylase. • Undergoes phosphorylation to form co-A by dephospho-coA kinase.
- 34. ROLE OF COENZYME-A IN DIFFERENT METABOLISM • Formation of acyl coA from free fatty acid which undergoes β-oxidation of fatty acid. • Formation of acetyl coA from pyruvate which is aerobically oxidized in TCA cycle. • Acetyl coA and malonyl-coA is used in synthesis and elongation of fatty acid. • Formation & utilisation of ketone bodies. • Cholesterol synthesis. • Formation of succinyl coA used for heme synthesis.
- 35. ADENOSINE 3′-PHOSPHATE 5′- PHOSPHOSULFATE(PAPS):BIOSYNTHESIS AND USES • Also known as ‘active sulphate’. • Sulphate(so₄² ̄) is activated in two steps to produce PAPS which further undergoes reduction to produce sulphide(S² ̄) for different sulfation reactions catalyzed by sulfotransferases.
- 36. FUNCTION OF PAPS • PAPS of ‘active sulfate’ is the sulfide donor for different reactions catalyzed by various sulfotransferases. • Important compounds which are conjugated with sulphate are- Proteoglycans. Steroid hormone. Glycolipids(sulfatide). Bilirubin. Various drugs. eg-minoxidil sulphate
- 37. SULPHATED PROTEOGLYCANS • HEPARIN-Fractionated form of heparan sulphate derived from mast cells. • It binds with antithrombin to inhibit thrombin. • Therapeutic agent used to inhibit coagulation. • CHONDROITIN SULPHATE- contribute to the tensile strength of cartilage, tendon, ligaments and wall of the aorta. • KERATAN SULPHATE-present in cornea, cartilage, bone and horny structures formed of dead cells. • DERMATAN SULPHATE- contribute to the pliability of the skin • Also present in blood vessels and heart valves.
- 38. SULFONATION OF STEROID HORMONE(DHEA-S) • DHEA-S(Dehydroepiandrosterone sulphate) is the sulfate ester of DHEA. This conversion is reversibly catalyzed by sulfotransferase (SULT2A1) primarily in the adrenals, the liver, and small intestine. • In the blood, most DHEA is found as DHEA-S with levels that are about 300 times higher than those of free DHEA as it is more stable. • Whereas DHEA levels naturally reach their peak in the early morning hours, DHEA-S levels show no diurnal variation. • From a practical point of view, measurement of DHEAS is preferable to DHEA, as levels are more stable(IN ADRENOGENITAL SYNDROME).
- 40. SUMMARY • Nucleotide co-enzymes are compounds having at least one simple nucleotide moiety in it’s structures. • Nicotinamide containing coenzyme NAD⁺ and flavoprotein take part in redox reactions of different metabolism while NADP takes part in reductive biosynthesis. • Non redox function is important for ADP-ribosylaton, drug therapeutics etc. • Flavoproteins like FMN or FAD is a part of COMPLEX I and COMPLEX II in ETC. • CoenzymeA takes part in different metabolisms like TCA cycle,β-oxidation of fatty acid, synthesis and elongation of fatty acid, cholesterol and heme synthesis etc. • PAPS or active sulfate is the sulfide donor for different sulfonation reactions catalyzed by different sulfotransferases forming sulfated product of immense biological significance.