Purine de novo synthesis, in LIVER, large energy expenditure (more than pyr de novo)1. Start with activated ribose (PRPP)2. Build on nitrogen base using simpler starting materials (aa/ATP/CO2/FH4) to synth ntsSALVAGE: reattach nitrogenous base to PRPP to synth nts

ReactantEnzymeProductNotes

1. ribose-5-phosphatePRPP synthase (5-phosphoribosylpyrophosphate synthase)5-phosphoribosyl-1-pyrophosphate (PRPPP)ATPAMPMG+2 cofactorDeficiency leads to Arts Syndrome in kidsActivated by PiInactivated by purine nts (AMP, GMP, IMP)1 high E bond (HEB)

2. PRPPPRPP glutamyl amidotransferase (stopped in lrg amts of AMP/GMP) (inhib by AMP/IMP/GMP, activated by PRPP)5-phosphoribosyl-1-amine (PRA, III)*******COMMITTED STEPglutamine (amide grp = Nu)glutamatePPi2Pi via pyrophosphatase (1 HEB)

3. PRAGlycinamide riboside synthetaseGlycinamide ribosyl-5-phosphate (GAR, IV)ATPADP+Pi (1 HEB)Glycine (-COO reacts with amino of PRA, III)PRPP pyrophosphate displaced by Gly amide NPurine atome C4, C5, N7 from Gly

4. GARFormyl transferaseFormylglycinamide ribosyl 5-phosphate (FGAR, V)Formyl grp of N10-formyl FH4 transferred to amino grp of Gly res of GAR, IVN10-formyl FH4tetrafolate(FH4) forming pur C8Inhibited by PABA analogs (sulfonamides): affect bacteria, not humans

5. FGARVI VynthetaseFormylglycinamidine ribosyl 5-phosphate (FGAM, VI)2nd Glutamine N donor, carbonyl O of FGAR replaced with NH2 amide of glutamineATP, Mg2+ cofactor1 HEB

6. FGAMVII SynthetaseAminoinidazole ribosyl-5-phosphate (AIR, VII)ATPH2O removed1 HEB

7. AIRVII carboxylaseAminoinidazole carboxylate ribosyl-5-phosphate (CAIR, VIII)C6 from CO2, used as HCO3

8. CAIRIX synthetaseAminoimidazole succinyl carboxamide ribosyl-5-phosphate (SAICAR, IX)ATPADP+PiPurine N1 from Asp1 HEB

9. SAICARAdenylosuccinaseAminoimidazole carboxamide ribosyl 5-phosphate (AICAR, X)C atoms of Asp are released as fumarateN1 from Asp joins with the imidazole ring

10. AICARFormyl transferase vFormimidoimidazole carboxamide ribsyl 5-phosphate (FAICAR, XI)Final purine C2 removedN10-formyl FH4FH4Inhibited by folic acid analogs (methotrexate: inhibits reduction of FH2FH4, trimethoprim: selectively inhibits dihydrofolate reductase)

11. FAICARIMP DH (inhib by mycophenolic acid, tiazofurin)Inosine monophosphate2nd ring closureH2O removed from formyl, carboxamide grpIMP rapidly converted to AMP & GMPJoins base hypoxathine joined by a glycosidic bond N9-C1

AMP Synthesis (7 HEB from ribose 5-PAMP)

1. IMPAdenylosuccinate synthetase (inhib by AMP)AdenylosuccinateC^ carbonyl O if IMP is substituted by amino grp of aspartateGTP

2. adenylsuccinateAdenylsuccinaseAdenosine monophosphate (AMP)Asp: N sourceGTP: energy

GMP Synthesis (8 HEB from ribose 5-PGMP)

1. IMPIMP DH (inhib by GMP)Xanthine monophosphate (NAD dependent) (XMP)

2. XMPGMP synthaseGuanosine monophosphate (GMP)Glu donates its amino N to the carbonyl O at C2 of XMPNAD+NADH (reduction)Ppi2Pi via pyrophosphataseInsufficient ATP leads to IMPGMPATP: energy, can be hydrolyzed further

ATP + AMPAdenylate kinase2 ADP

ATP + GMPGuanylate kinaseGDP + ADP

ATP + G/CDPNucleoside diphosphate kinaseGTP or CTP + ADP

Purine bases (xanthine, guanine) Hypoxanthine-guanine phosphoribosyl transferase (HGPRT) (competitive inhib IMP/GMP)IMP, GMPPRPP: sourece of ribose 5-phosphateDeficiency: Lesch-Nyhan Syndrome

Adenine Adenine phosphoribosyl transferase (APRTase) (compet inhib: adenine)AMPPRPP: sourece of ribose 5-phosphate

Adenosine + ATPAdenosine kinase (5-phosphotranferase)AMP

Degradation of Purine Bases

AMPAMP deaminaseIMP

AMP/GMP/IMP5nucleotidaseAdenosine/guanosine/inosine

AdenosineAdenosine deaminaseInosineDef of adenosine deaminase = severe combined immunodeficiency (SCID)

GuanineGuanase/guanine deaminaseXanthine

HypoxanthineXanthine oxidase (inhib by allopurinoloxypurinol)XanthineO2H2O2 (reduced)H2O2H2O+O2 via catalase

XanthineXanthine oxidaseUric acid

Pyrimidine De Novo Synthesis (less energy expenditure)1. Build nitrogen base using simpler starting materials (aa/ATP/CO2/FH4)2. Add PRPP to synth nts

1. HCO3-Carbamoyl phosphate synthase (CPSII) (activated by PRPP, inhib by ATP/UTP/CTP)CarboxyphosphateATPADP

1a. carboxyphosphateCarbamic acidNH3 (ammonia) from Glu side chain

1b. carbamic acid********CSPII, ATCase, dihyrdoorotase are domains of a sungle multycatalytic peptide chainCarbamoyl phosphateATP*********REGULARE STEPCO2 provides C2Glu N32 HEB

2. carbamoyl phosphateAspartate transcarbomylase (ATCase) (activated by ATP/GTP, inhib by CTP)Carbomoyl aspartic acid (CAA)-amino Asp condenses donates C4, C5, C6, N1*******COMMITTED STEPno E input

3. CAADihydroorolaseDihydroorotic acid (DHOA)Closed hydrolyticallyH2oO released btw middle amide grp of carbomoyl & -carboxyl Asp

4. DHOADihyroorotate DH (DHODH) (inhib by Leflunomide-immunosuppresive for rheumatoid arth)Orotic acid (OA, orotate)

5. OAOrotate phosphoribosyl transferase******OPT & OAD belong to domains of a single multicatalytic polypep chain, def causes type I orotic acid aciduria, both inhib by allopurinolOrotidine 5-monophosphate (OMP)Completed pyr ring attached to ribose 5-P from PRPP (also precursor for His and Trp)PPi released (irreversible) PPi2Pi via pyrophosphatase (1 HEB)3 HEB in OMP synth from Glu & CO2

6. OMPOrotidylic acid decarboxylase (inhib by UMP) def causes type II orotic acid aciduriaUridine monophosphate (UMP) (RNA precursor)3 HEB in UMP formation from Asp & CO2

7. UMPNucleotide monophosphate kinase (UMP kinase)Uridine diphosphate (UDP)ATPADP+Pi

8. UDPNucleotide diphosphate kinaseUridine triphosphate (UTP)ATPADP+Pi

9. UTPCTP synthase (activated by ATP/GTP, inhib by CTP)Cytidine triphosphate (CTP)Glutamine amine donor (NH4 can also be donor) replaces carbonyl of UTPCannot occur at monophosphate levelGlutamineglutamateATPADP+Pi

10. UDPNADPH-dependent ribonucleotide reducatase (2 subunits, regulated by dTTP, inhib by dATP, 6-azaruridine: anticancer, hydroxyurea) (in presence of thioredoxin: red agent w/2 free sulfhydryl (-SH2) grps to facilitate easy forming of DISULFIDE BOND, thioreductasedisulfide via oxidation, thioredoxin reductase regenerates red thioredoxin))Deoxyuridine diphosphate (dUDP) (can be phosphorylated to triphosphate to make dUTPs for DNA synth)Reduced to deoxyribose occurs at DIphosphate levelUDP reduced at 2 C (OH becomes H)

11. dUDPNucleotidasedUMPDephosphorylation

12. dUMPThymidylate synthase (activated by ATP/GTP, inhib by CTP, 5-fluorouracil: anticancer)5-fluorouridine triphosphate (FUMPdFUMP substrate inhibitor of dUMP at thymidylate synthase active site, form fFUM-FH4, dTMP/dTTPdTMPdUMP methylated @C5methyl grp source: N5-N10-methylene FH4 (1C grp transfer)methylene grp reduced to methyl grp by FH4FH2FH4 via dihydrofolate reductase (inhib by methotrexate) w/NADPH as reductant (reduced)Must regen FH4 to synth more thymydilate

13. dTMPNucleotide monophosphate kinasedTDPATP

14. dTDPNucleotide diphosphate kinasedTTP (precursor dor DNA synth, regulates ribonucleotide reductase)ATP

Degradation of pyrimidine in LIVER, leads to H2O soluble compounds (-alanine, BAIB)

Phase 1

1. Pyrimidine ntsNonspecific phosphatasesNucleosidesdephosphorylation

2. nucleosidesCleavage enzFree pyr bases (cytosine, uracil, thymine)

Phase 2

2a. CytosineNADPH-dependent DHDihydrouracilReduced

DihydrouracilDihydropyrimidinase or hydratase-ureidopropionateHydrated

-ureidopropionate-ureidopropionaseCO2, NH3, -alanine

2b. ThymineNADPH-dependent DHDihydrouracilReduced

DihydrouracilDihydropyrimidinase or hydratase-ureidopropionateHydrated

-ureidopropionate-ureidopropionaseCO2, NH3, -aminoisobutyrate (BAIB)

Phase 3

3a. -alanine (from cytosine)Transaminase (+activation)Malonyl CoACO2/de novo synth of FA/synth of CoEnz A/carnosine

3b. -aminoisobutyrate (BAIB) (from thymine)Transamincase (+activation)Methylmalonyl CoAsuccinyl CoA to Krebs

NAD Synthesis

1. Nicotinamide (derive of niacin-Vit B3)Nicotinamide phsophoribosyl transferaseNicotinamide mononucleotideNicotinamide condenses with PRPP (ribose 5-P donor)PPi released

2. nicotinamide mononucleotideNAD-pyrophosphorylaseNicotinamide adenine dinucleotide (NAD)P of ATP of nicotinamide mononucleotide

3. NADPhosphorylating enzNADPP by ATP

FMN/FAD Synthesis (for reversible redox rxns)

1. Riboflavin (from Vit B2)Riboflavin kinaseRiboflavin phosphate (flavin mononucleotide, FMN)ATP

2. FMNFAD-pyrophosphorylaseFlavin adenine dinucleotide (FAD)ATP

CoEnz A Synthesis (component of acetyl CoA)

1. Panthothenate (Vit B5)Panthothenate kinase4-phosphopanthothenateATP

2. 4-phosphopanthothenate + Cys(ATP dep) phosphopanthothenoylcysteine synthetase4-phosphopanthenoylcysteineATP

3. 4-phosphopanthenoylcysteinephosphopanthothenoylcysteine decarboxylase4-phosphopantotheinedecarboxylation

4. 4-phosphopantotheineDephospho-CoA pyrophosphorylaseDephosphoconezyme AP

5. dephosphocoenzyme A(ATP dep) dephospho-CoA kinaseCoEnz AP

Folic acid analogs: methotrexate (MTX), trimethoprim Dihydrofolate analog: amethopterin Purine analogs: 1,6-mercaptopurine, acyclovir (acylcloguanosine), adenine arabinoside (Ara-A), 2-3-dideoxyinosine Hypoxanthine analog: allopurinol Pyrimidine nucleoside analogs: 5-fluorouracil, 6-azuradine, arabinosyl cytosine (Ara-C) cytosine arabinoside 5-triphosphate interferes with DNA rep, 3-azido-5deoxythymidine (azothymidine, AZT) Glutamine analogs: azaserine, acividin Degradation products of pyrimidine: -alanine, -aminoisobutyrate