ATP? Depends on the system….

1 ATP – Glucose to G-6-P   Ribose-5-P 1 ATP – But 2 high energy bonds to get to PRPP 4 ATP – In vertebrates to get onto IMP from PRPP 5 ATP – In prokaryotes to get onto IMP from PRPP The pentose phosphate shunt can go back through glycolytic pathways, utilizing another ATP (Fructose-6-P to Fructose-1,6,bisP and then onto Ribose-5-P), but not necessary to generate Ribose-5-P)

Pyrimidine Metabolism and Cancer Therapy

LEARNING OBJECTIVES Nomenclature of pyrimidines* Key features of biosynthetic pathway and origin of atoms in pyrimidine ring Basis of chemotherapy using nucleotide analogs *Key words are highlighted in yellow

Pyrimidine Synthesis The pyrimidine ring is completely synthesized, then attached to a ribose-5-phosphate donated by PRPP Source of carbons and nitrogens less diverse than with purines.

(Carbamoyl-P)

Urea Synthesis Pyrimidine Synthesis

Carbamoyl Phosphate Synthase and Channeling of Intermediates Miles et al. J. Biol. Chem. 274, 12193-12199 (1999)

Enzymatic functions from one large protein (215,000 Mr)

What to Know Compare and contrast CPS I and CPS II CPSII, aspartate transcarbamoylase, and dihydroorotase are three enzymatic functions in one protein. Oratate phosphoribosyltransferase and OMP decarboxylase are two enzymatic functions in one protein. Deficiency leads to Orotic Aciduria. Know symptoms and how to treat. Orotate is made and then attached to a PRPP.

UMP UDP UTP Nitrogen Donor (again!) Uridine Cytidine Uridine monophosphate kinase Uridine diphosphate kinase Nitrogen Donor (again!) Uridine Cytidine

inhibits this reaction Thymidylate synthase is a major target for anti-cancer therapy. See Figs 26.25-26.27 in reading for more details 5-fluorouracil Methotrexate also inhibits this reaction

Regulation of Pyrimidine Synthesis

Pyrimidine Breakdown

De novo purine synthesis AMP GMP ADP ATP GDP GTP Adenosine monophosphate kinase diphosphate Guanosine IMP De novo pyrimidine synthesis UMP UDP Uridine monophosphate kinase UTP Uridine diphosphate kinase CTP dUDP dUMP dTMP Thymidylate synthase dTDP dTTP Thymidine monophosphate kinase Thymidine diphosphate kinase

Ribonucleotides to Deoxyribonucleotides Very Important!

Ribonucleotides to Deoxyribonucleotides

Logic For Deoxynucleotide Synthesis (Fig 26.24) in reading High [ATP], plenty of energy, ok to make DNA High [ATP] means the ribonucleotide reductase is active (ON) ATP in specificity site S favors CDP or UDP in catalytic site C  [dCDP] and [dUDP] ↑ dCDP and dUDP become metabolized to dTTP (thus justifying the synthesis of dUMP even though it does not get incorporated into DNA) As [dTTP]↑, it will begin to occupy specificity site favoring GDP in catalytic site, thus leading to [dGP]↑  [dGTP]↑ As [dGTP]↑ it begins to occupy specificity site and thus favor ADP in catalytic site, leading to [dADP]↑  which will replace ATP in activity site and turn enzyme off

Uracil Analogues in Cancer Therapy 5-fluorouracil β-D-arabinofuranosylcytosine (Ara-C)

Cancer Therapy with 5-fluorouracil 5-FU is typically given with thymidine to boost its effectiveness 5-FU is converted to dFUMP dFUMP inhibits Thymidylate synthase In cancer cells, 5-FU is also incorporated into RNA 5-FU in RNA is detrimental to cancer cells Inhibition of Thymidylate synthase is detrimental to both cancer and normal cells So, administration of thymidine protects both normal and cancer cells, but 5-FU in cancer cells kill them O F HN N HO 2-O3POH2C dFUMP dUMP dTMP Thymidylate Synthase

Thymine Analogues in Cancer Therapy Thymidine Bromodeoxyuridine Trifluorothymidine

Purine Analogues in Cancer Therapy Hypoxanthine 6-mercaptopurine 6-thioguanine Purines are used as free bases or nucleosides, as nucleotides are poorly transported across the membrane.