BICH 411 1st Edition Lecture 21 Outline of Last Lecture I. Amino acid formationII. Amino acid inhibitor herbicidesIII. Amino acid catabolismIV. Inborn Errors of MetabolismOutline of Current Lecture I. Purine synthesisII. Purine degradationIII. Pyrimidine SynthesisIV. Pyrimidine DegradationCurrent Lecture-the ribose of nucleotides can be source of energy (think pentose phosphate pathway)-the purine and pyrimidine rings can’t be used for energyPurine Synthesis-N1 is from aspartate, two other nitrogens (N3 and N9) are from glutamine-C4, C5, and N7 come from glycine-C6 is from CO2-C2 and C8 are from THF**figure 26.2 would be a good quiz question**-IMP is a precursor for AMP and GMPStep 1: ribose-5-phosphate is activated by ATP-dependent pyrophosphate addition (PPi) which makes PRPP. Ribose-5-Phosphate pyrophosphokinase is the enzyme in this reaction.Step 2: 5-phosphoribosyl-alpha-pyrophosphate (PRPP) + glutamine + H2O Phosphoribosyl-beta-amine + glutamate + PP. The enzyme for this is glutamine: PRPP amidotransferase. This is the committed step**These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Step 3: Phosphoribosyl-beta-amine + glycine + ATPGlycinamide ribonucleotide (GAR) + ADP + Phosphate. The enzyme is GAR synthetase. (Remember synthetases require ATP, synthases don’t.) Step 4: GAR + N10-formyl-THF  FGAR + THF. The formyl group of N10-formyl-THF transfers to GAR to form formylglycinamide ribonucleotide (FGAR). GAR transformylase is the enzyme. Step 5: FGAR + ATP + Glutamine + H2O  FGAM + ADP + glutamate + P. This forms formylglycinamide ribonucleotide (FGAM) with the enzyme FGAM synthetase. It essentially swaps the carbonyl for N. Step 6: FGAM + ATP  AIR + ADP + P. This forms 5-Aminoimidazole Ribonucleotide (AIR) with the enzyme AIR synthetase. (This reaction is similar to step 5). The first ring is built so now we need to build the second ring. Step 7: AIR + CO2 + ATP  CAIR + ADP + P. This is a carboxylation reaction using AIR carboxylase to form Carboxyaminoimidazole ribonucleotide (CAIR). Step 8: CAIR + aspartate + ATP  SAICAR + ADP + Pi. This uses the enzyme AICAR transformylaseto form N-succinylo-5-aminoimidazole-4-carboxamide ribonucleotide (SAICAR). Step 9: SAICAR  AICAR + fumarate. Adenylosuccinate lyase causes a cleavage of fumarate. Fumarate then proceeds to the TCA cycle.Step 10: AICAR + N10-formyl-THF  FAICAR + THF. This reaction adds a carbon using the enzyme AICAR transformylase. Step 11: FAICAR  IMP + H2O. An amino group attacks the formyl group to close the second ring, forming inosine monophosphate (IMP). The enzyme involved is IMP synthase. **6 ATPs are used in all. 5 in the reaction, and 1 for the pyrophosphorylation  good exam question-Azaserine is an irreversible inhibitor of enzymes that rely on glutamine. It binds to the glutamine binding sites. -Tetrahydrofolate (THF) carries one-carbon units. (except CO2 – biotin carries this!!) **this wouldbe a good exam question**-Folate analogs are used as purine inhibitors for bacteria and tumors. Sulfanamides are good against bacteria. Methotrexate and aminopterin are good chemotherapeutic agents.-AMP and GMP are formed from IMP. (GTP is the energy for AMP formation, while ATP is the energy for GMP formation)-AMP formation: step 1: IMP + Aspartate + GTP Adenylosuccinate + GDP + P using adenylosuccinate synthetase. Step 2: Adenylosuccinate  AMP + fumarate using adenylosuccinate lyase.***This kind of reaction was seen in IMP formation.-GMP formation: step 1: IMP + NAD+ + H2O  XMP + NADH + H using IMP dehydrogenase.Step 2: XMP + ATP + Glutamine + H2O  GMP + AMP + PP + Glutamate(this last step is identical to the first two steps of IMP synthesis)-Purine biosynthesis is regulated at several steps (see figure 26.6)-to save purines, hypoxanthine and guanine are recombined with PRPP to form more nucleotides – this is the HGPRT pathway (figure 26.7 shows this pathway)(without this pathway, retardation and arthritis occur  Lesch-Nyhan syndrome.)-Severe combined immunodeficiency syndrome (SCID) has an absence of adenosine deaminase. Purine Degradation-purines are degraded to uric acid.-nucleotidases change nucleotides to nucleosides-nucleosides are degraded by purine nucleoside phosphorylase (PNP)-the products are changed to xanthine by guanine deaminase and xanthine oxidase(see figure 26.8)-AMPIMP with AMP deaminase is the purine nucleoside cycle which converts aspartate to fumarate. Fumarate then continues on to the TCA cycle (anapleurosis).-Gout is a disease that occurs when uric acid accumulates. Allopurinol inhibits xanthine oxidase and is used to treat gout.Pyrimidine Synthesis-unlike purines, the ring is made before ribose-5-phosphate is involved.-Carbamoyl-phosphate and aspartate are the precursors!-Carbamoyl-phosphate synthetase II (CPS-II) is cytostolic. (remember CPS-I is in the mitochondria)**figure 26.13 shows the atom sources in pyrimidines  good quiz question!!-Step 1: CPS-II forms carbamoyl phosphate from HCO3-, 2 ATP, and glutamine.**this is the committed step since it’s the only purpose for carbamoyl phosphate – good test question!!Step 2: Aspartate transcarbamoylase (ACT) works to form carbamoyl-aspartate.Step 3: Dihydroorotase closes the ring and removes a water.Step 4: the pyrimidine (orotate) is formed by DHO dehydrogenaseStep 5: Orotate forms orotidine-5’-phosphate with Orotate phosphoribosyltransferase. Note that the ribose-P comes from PRPP!Step 6: UMP is formed with OMP decarboxylase-metabolic channeling occurs using a multifunctional polypeptide enzyme. What is the advantage?**Answer would make a good test question! (Check book)-UMPUDPUTP using nucleoside monophosphate/diphosphate kinase. CTP is formed from UTP and ATP using CTP synthetase.Pyrimidine Degradation-pyrimidines are reused to form more nucleotides using phosphoribosyltransferase. -Catabolism of cytosine and catabolism of thymine are not good energy sources!! (cytosine breakdown forms beta-alanine, ammonium, and CO2. Thymine breakdown forms beta-aminoisobutyric acid, ammonium, and CO2.)-If the 2’ position is reduced, the nucleotide goes to DNA synthesis! This occurs with ribonucleotide reductase and forms dNTP. It maintains a balance of all the dNTPs (dATP, dGTP, dCTP, and dTTP). -The catalysis of the enzyme is turned off and on for regulation. ATP