1. ATP?
Depends on the system….

4. 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)

5. Pyrimidine Metabolism and Cancer Therapy

6. 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

7. 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.

8. (Carbamoyl-P)

10. Urea Synthesis
Pyrimidine Synthesis

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

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

13. 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.

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

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

16. Regulation of Pyrimidine Synthesis

17. Pyrimidine Breakdown

18. 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

19. Ribonucleotides to Deoxyribonucleotides
Very Important!

20. Ribonucleotides to Deoxyribonucleotides

21. 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

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

23. 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

24. Thymine Analogues in Cancer Therapy
Thymidine
Bromodeoxyuridine
Trifluorothymidine

25. 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.