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Amino Acid met abolism
A mino acids
Folat e met abolism
Met hylene
THF
Glu, Gln,
Asp , NH3
Met
Cycle
Urea
oxaloacet at e
Pu r in e s
Uric Acid
DNA
RNA
Py r im id in e s
( energy)
f um arat e
TCA Cycle
Nucleic Acid met abolism
Nucleic Acid met abolism
Click on any blue rect angle t o see det ails.
Carbamoyl
Phosphate
am i n o a c id s,
f o la t e
Purine
Salvage
PRPP
Purine
Biosynt hesis
IMP
Pyrimidine
Biosynt hesis
OMP
Pyrimidine
Salvage
Pyr im idine MP
Pur ine MP
Ribonucleot ide
reduct ase
Ribonucleot ide
reduct ase
dNTP
NTP
Purine
Degradat ion
DNA
RNA
dNTP
NTP
Pyrimidine
Degradat ion
NH4
Uric A cid
( energ y )
Formation of PRPP: Phosphoribose pyrophosphate
O
PO
O
P O
O P O P
OH
OH OH
ribose - 5 - phosphate
ATP
OH OH
phosphoribose - 1
pyrophosphate
AMP
PRPP Use in Purine Biosynthesis:
PO
H2O
O
OH
P O
OH
O
NH2
O PO P
phosphoribose - 1
pyrophosphate
glutamine
glutamate
OH
OH
O
N
HN
The First Purine: Inosine Monophosphate
(folates are involved in this synthesis)
O
P O
OH
Conversion to Adenosine:
O
GTP
N
HN
NH 2
GDP + Pi
N
N
N
N
N
N
ribose-5-P
aspartate
fumarate
Inosine monophosphate
ribose-5-P
Adenosine monophosphate
Conversion to Guanosine:
O
NAD
+
+
N
HN
N
N
ribose-5-P
Inosine monophosphate
N
N
O
H2O
ATP
O
NADH + H
N
H
ribose-5-P
O
AMP + PPi
N
HN
N
gln
Xanthosine monophosphate
glu
N
N
NH
2
N
N
ribose-5-P
Guanosine monophosphate
OH
Nucleoside Monophosphate Kinases
AMP + ATP <--> 2ADP
(adenylate kinase)
GMP + ATP <---> GDP + ADP
(guanylate kinase)
• similar enzymes specific for each nucleotide
• no specificity for ribonucleotide vs. deoxyribonucleotide
Ribonucleotide Reductase
P OP O
O
Enzyme•
NADH
Enzyme
NAD+
OH
OH
P OP O
X
X
O
OH
H
Hydroxyurea inhibits this enzyme: chemotherapeutic use
O
HONH C NH 2
Regulation of Ribonucleotide Reductase
A TP
+
CDP
(-)
dCDP
dCTP
(-)
dUDP
dTTP
+
dGDP
dGTP
dADP
dATP
A TP
+
UDP
GDP
+
ADP
(-)
Nucleoside Diphosphate Kinase
N1DP + N2TP <--> N1TP + N2DP
dN1DP + N2TP <--> dN1TP + N2DP
• No specificity for base
• No specificity for ribo vs deoxy
Feed-forward regulation by PRPP
PRPP
IMP
A TP
GTP
GMP
AMP
GTP
ATP
Feed-forward regulation by PRPP
PRPP
+
IMP
A TP
GTP
GMP
AMP
GTP
ATP
Feed-forward regulation by PRPP
PRPP
IMP
A TP
GTP
+
+
GMP
AMP
GTP
ATP
Feed-forward regulation by PRPP
PRPP
+
-
-
IMP
ATP
GTP
GMP
AMP
GTP
ATP
Degradation of the Purine Nucleosides:
NH 2
HO
2
+
4
N
N
N
N
ribose
O
NH
N
HN
Adenosine
deaminase
(ADA)
ribose
purine nucleoside
phosphorylase
N
N
H
Hypoxanthine
Inosine
Adenosine
N
HN
N
N
O
ribose - 1 - P
Pi
xanthine
oxidase
Pi
O
N
HN
NH 2
N
N
ribose
Guanosine
ribose - 1 - P
O
N
N
H
O
+
NH 4
N
HN
purine nucleoside NH
2
phosphorylase
H 2O
N
HN
Guanine
deaminase
O
N
H
N
H
Xanthine
Guanine
xanthine
oxidase
O
HN
O
Uric acid
O
H
N
N
H
N
H
“Salvage” Pathways for Purine Nucleotides
O
N
HN
N
H
N
O
Hypoxanthine
+
P O
Hypoxant hineguanine
phosphoribosyl
t ransf erase
OH OH
PRPP
N
P O
O
O P O P
N
HN
N
O
+
PPi
OH OH
Inosine monophosphate
APRT - Adenine phosphoribosyl transferase performs a similar function with adenine.
Adenosine Deaminase Deficiency:
NH 2
Adenosine
deaminase
(ADA)
O
OH
H
O
N
HN
N
N
HO
O
N
N
N
N
2-deoxyribose
N
HN
N
N
H
Deoxyinosine
Hypoxanthine
Guanine
Xanthine
Deoxyadenosine
dAMP
dADP
Uric acid
dATP
O
Gout: deposition of urate crystals in joints,
“tophi” in cooler periphery
N
HN
N
H
N
Hypoxanthine
Hyperuricemia can be caused by:
xanthine
oxidase
Accelerated degradation of purines:
O
N
HN
O
•Accelerated synthesis of purines
•Increased dietary intake of purines
N
H
N
H
Xanthine
xanthine
oxidase
O
HN
O
Impaired renal clearance of uric acid
H
N
OH
O
N
H
N
H
Uric acid
Allopurinol inhibits xanthine oxidase
and reduces blood uric acid levels:
N
H
N
N
N
Allopurinol
The hands of a patient with a long history of gout, including high serum urate levels
BY: Univ. of Alabama at Birmingham, Dept. of Pathology
http://creativecommons.org/licenses/by-nc-sa/3.0/deed.en
Lesch-Nyhan Syndrome: Defective HGPRT
• hyperuricemia
• spasticity
• mental retardation
• self-mutilation behavior
O
N
HN
N
H
N
O
Hypoxanthine
+
P O
Hypoxant hineguanine
phosphoribosyl
t ransf erase
OH OH
PRPP
N
P O
O
O P O P
N
HN
N
O
+
PPi
OH OH
Inosine monophosphate
A defect in APRT does NOT have similar consequences
Myoadenylate Deaminase ‘Fills’ the TCA Cycle in Muscle
H 2O
NH3
myoad enylat e
d eaminase
NH 2
O
N
N
N
HN
N
N
N
N
ribose-5-P
Adenosine monophosphate
ribose-5-P
Inosine monophosphate
Asp, GTP
Fumarate
GDP + Pi
To
TCA
Cycle
Carbamoyl phosphate synthetase II - a cytoplasmic enzyme…
O
2 ATP + HCO3 +
glut amine + H 2O
2-
NH2
OP
C
+ glut amat e + 2A DP + Pi
carbamoyl
phosphat e
…used for pyrimidine synthesis
O
O
NH2
O
C
2-
OP
carbamoyl
phosphate
O
C
+
-
CH2
CH
NH
+ 3
aspartate
-
CO2
O
O
C
O
NH2
CH2
C
CH
N
H
HN
-
CO2
O
N
H
orotate
CO2
Orotate is linked to PRPP to form Uridine monophosphate:
O
HN
O
O
N
H
CO2
HN
orotate
O
+
P O
P O
O
O P OP
OH OH
phosphoribose - 1
pyrophosphate
O
HN
N
CO2
O
O
OH
P O
OH
orotidine
monophosphate
N
O
CO2
OH
OH
uridine
monophosphate
Newly-synthesized uridine monophosphate will be phosphorylated to
UDP and UTP, as described for the purine nucleotides.
UTP can be converted to CTP by CTP Synthetase:
O
NH 2
HN
O
P OP O P O
N
N
gln
glu
O
OH
O
P OP O P O
OH
uridine
triphosphate
ATP
+
H 2O
ADP
+
Pi
N
O
OH
OH
cytidine
triphosphate
Some UDP is converted to dUDP via ribonucleotide reductase.
UDP
ribonucleotide
reductase
dUDP
dUTP
ADP
ATP
dUMP
H 2O
Pi
The Thymidylate Synthase Reaction:
O
O
HN
O
P O
CH3
HN
N
O
O
P O
thymidylate synthase
OH H
deoxyuridine
monophosphate
N 5, N10
methylene
tetrahydrofolate
dihydrofolate
DHFR
****
methylene
donor
THF
NADH
NAD+
N
O
OH H
deoxythymidine
monophosphate
Methotrexate Inhibits Dihydrofolate Reductase:
O
O
HN
O
P O
CH3
HN
N
O
O
OH H
deoxyuridine
monophosphate
N 5, N10
methylene
tetrahydrofolate
O
P O
thymidylate synthase
dihydrofolate
DHFR
****
N
OH H
deoxythymidine
monophosphate
NADH
X Met ho t rexat e
methylene
donor
THF
NAD+
Dihydrofolate builds up, levels of THF become limiting,
thymidylate synthase is unable to proceed. Follow it with
a dose of Leucovorin, a.k.a. formyl-THF.
FdUMP Inhibits The Thymidylate Synthase Reaction:
O
F
HN
O
P O
O
N
O
O
OH H
5-fluorodeoxyuridine
monophosphate
(F-dUMP)
P O
thymidylate synthase
X
N 5, N10
methylene
tetrahydrofolate
dihydrofolate
DHFR
****
methylene
donor
CH3
HN
THF
NADH
NAD+
N
O
OH H
deoxythymidine
monophosphate
Complicated Pathways for Pyrimidine Production:
dCTP
CTP
dCDP
CDP
***
***
UTP
dUTP
dTTP
UDP
dUDP
dTDP
dUMP
dTMP
UMP
de-novo synthesis
***
***
OMP
This figure is primarily a study aid; you do not need to memorize it or reproduce it.
The information here merely summarizes material from previous sections.
Pathologies of pyrimidine nucleotide biosynthesis:
Orotic acidurea due to OTC deficiency - please
review your Urea Cycle notes.
Hereditary orotic acidurea - deficiency of the
enzyme that convert orotate to OMP to UMP.
Not common.
Pyrimidine degradation:
Cytidine deaminase converts cytidine to uridine
O
NH2
HN
N
O
O
HO
OH
N
cyt idine
deaminase
O
O
HO
OH
OH
Cytidine
N
OH
Uridine
A phosphorylase removes the sugar
O
O
CH3
HN
HO
O
O
OH
N
H
(deoxy)thymidine
CH3
HN
+
Pi
O
pyrimidine
phospho rylase
N
H
thymine
+
HO
O
OP
OH H
deoxyribose-1-phosphate
Degradation of the base proceeds (products are
unimportant here)
Pyrimidines can be salvaged as well:
Enzyme: Pyrimidine nucleoside phosphorylases
Thymine + deoxyribose-1-phosphate --> thymidine
(NOT thymidine monophosphate!)
O
O
CH3
HN
HO
O
O
OH
N
H
CH3
HN
+
Pi
O
pyrimidine
phospho rylase
N
H
thymine
+
HO
(deoxy)thymidine
O
OP
OH H
deoxyribose-1-phosphate
Enzyme: Thymidine kinase - adds the monophosphate back
Thymidine + ATP --> thymidine monophosphate
Herpes Simplex Virus carries its own tk gene
Certain drugs act via the pyrimidine salvage pathway:
G
HO
O
H
G
HSV
thymidine
kinase
O
P O
H
H
H
AcycloGMP
Acyclovir
O
O
O
F
HN
N
H
5-fluorouracil
HO
O
HO
OP
OH H
deoxyribose-1-phosphate
F
HN
pyrimidine
phosp horylase
+
O
F
HN
O
O
N
uridine
kinase
PO
OH
O
O
H
fluorodeoxyuridine
OH
N
H
fluorodeoxyuridine monophosphate
(FdUMP)
5-FU efficacy depends on rate of degradation vs activation
O
O
O
F
HN
N
H
5-fluorouracil
O
HO
OP
5-FU
O
O
uridine
kinase
N
PO
OH
OH H
deoxyribose-1-phosphate
O
O
H
OH
fluorodeoxyuridine
-->
F
HN
pyrimidine
phosp horylase
+
HO
O
F
HN
-->
N
H
fluorodeoxyuridine monophosphate
(FdUMP)
FdUMP
+ methylene-THF + Thymidylate Synthase
--> inactivation of TS
Degradation
(via dihydropyrimidine dehydrogenase, DPD
DPD inhibitors can potentiate 5FU activity
Capecitabine mode of action:
O
HN
F
N
O
O
N
OH
cyt idine
deaminase
dealkylat ion
O
HO
CH3
O
pyrimidine
pho shorylase
F
HN
O
N
H
fluorouracil
OH
capecitabine
Cytosine arabinoside (araC) activation and inactivation:
O
NH2
HN
HO
O
O
NH2
N
N
OH
OH
Uridine arabinoside
(INACTIVE)
cyt id ine
deaminase
HO
O
O
N
N
cyt id ine
kinase
OH
OH
Cytosine arabinoside (araC)
PO
O
O
N
OH
OH
Cytosine arabinoside monophosphate
(ACTIVE)