section 8. amino acid metabolism urea cycle 11/18/05
TRANSCRIPT
Section 8. Amino Acid Metabolism
Section 8. Amino Acid Metabolism
Urea cycleUrea cycleUrea cycleUrea cycle
11/18/0511/18/05
Substrates for the Urea CycleSubstrates for the Urea Cycle
• Above, amino groups are transferred to glutamate, Above, amino groups are transferred to glutamate, from which ammonium is produced, and then used to from which ammonium is produced, and then used to make make carbamoyl phosphatecarbamoyl phosphate..
• Below, amino groups are transferred to produce Below, amino groups are transferred to produce aspartateaspartate..
• Above, amino groups are transferred to glutamate, Above, amino groups are transferred to glutamate, from which ammonium is produced, and then used to from which ammonium is produced, and then used to make make carbamoyl phosphatecarbamoyl phosphate..
• Below, amino groups are transferred to produce Below, amino groups are transferred to produce aspartateaspartate..
-amino acid
-keto acid
-ketoglutarate
glutamate NAD+
NADH
H2N-CO-OPO32-
-amino acid
-keto acid
-ketoglutarate
glutamate oxaloacetate
aspartate
1
Urea CycleUrea Cycle • Aspartate and Aspartate and carbamoyl carbamoyl phosphate phosphate each deliver an each deliver an amino group to amino group to the cycle.the cycle.
• Notice that the Notice that the carbamoyl carbamoyl phosphate phosphate production and production and condensation condensation occur in the occur in the mitochondrial mitochondrial matrix.matrix.
• Aspartate and Aspartate and carbamoyl carbamoyl phosphate phosphate each deliver an each deliver an amino group to amino group to the cycle.the cycle.
• Notice that the Notice that the carbamoyl carbamoyl phosphate phosphate production and production and condensation condensation occur in the occur in the mitochondrial mitochondrial matrix.matrix.
2
Fig. 23.16
NH4+ from Oxidative Deamination of GlutamateNH4+ from Oxidative Deamination of Glutamate
• Hexameric glutamate dehydrogenase is is controlled Hexameric glutamate dehydrogenase is is controlled allosterically.allosterically.– High energy levels inhibit (ATP and GTP).High energy levels inhibit (ATP and GTP).– Low energy levels activate (ADP and GDP).Low energy levels activate (ADP and GDP).
• NADPNADP++ can replace NAD can replace NAD++..
• NHNH44++ , which is toxic to humans, is produced in the , which is toxic to humans, is produced in the
mitochondria and used to make carbamoyl phosphate.mitochondria and used to make carbamoyl phosphate.
• Hexameric glutamate dehydrogenase is is controlled Hexameric glutamate dehydrogenase is is controlled allosterically.allosterically.– High energy levels inhibit (ATP and GTP).High energy levels inhibit (ATP and GTP).– Low energy levels activate (ADP and GDP).Low energy levels activate (ADP and GDP).
• NADPNADP++ can replace NAD can replace NAD++..
• NHNH44++ , which is toxic to humans, is produced in the , which is toxic to humans, is produced in the
mitochondria and used to make carbamoyl phosphate.mitochondria and used to make carbamoyl phosphate.
-ketoglutarateglutamate
glutamate dehydrogenase
NADH + H+ NAD+
NH4+
OO
CH2
O
CH2
O O
OO
CH2
CH2
NH3
+
O O
H
+
3
Carbamoyl Phosphate SynthesisCarbamoyl Phosphate Synthesis
• Carbamoyl phosphate synthetase is in mitochondrial matrix.Carbamoyl phosphate synthetase is in mitochondrial matrix.• NHNH44
++ is source of NH is source of NH33..• The hydrolysis of two ATP make this reaction essentially The hydrolysis of two ATP make this reaction essentially
irreversible.irreversible.• N-acetyl glutamate is an allosteric activator. (see S08L05)N-acetyl glutamate is an allosteric activator. (see S08L05)
• Carbamoyl phosphate synthetase is in mitochondrial matrix.Carbamoyl phosphate synthetase is in mitochondrial matrix.• NHNH44
++ is source of NH is source of NH33..• The hydrolysis of two ATP make this reaction essentially The hydrolysis of two ATP make this reaction essentially
irreversible.irreversible.• N-acetyl glutamate is an allosteric activator. (see S08L05)N-acetyl glutamate is an allosteric activator. (see S08L05)4
(p. 645)
1. ARGININOSUCCINATE SYNTHASE 2. ARGININOSUCCINASE1. ARGININOSUCCINATE SYNTHASE 2. ARGININOSUCCINASE3. ARGINASE 4. ORNITHINE TRANSCARBAMOYLASE3. ARGINASE 4. ORNITHINE TRANSCARBAMOYLASE1. ARGININOSUCCINATE SYNTHASE 2. ARGININOSUCCINASE1. ARGININOSUCCINATE SYNTHASE 2. ARGININOSUCCINASE3. ARGINASE 4. ORNITHINE TRANSCARBAMOYLASE3. ARGINASE 4. ORNITHINE TRANSCARBAMOYLASE
ATP
AMP + PPi
H2O
+
+
aspartate
UREA
carbamoylphosphate
fumaratearginine
argininosuccinate
ornithine
citrulline
UREACYCLE
1
23
4
2 Pi
H2N
Pi +
CH2
CH2
CH2
NNH2
NH2
+
OO
NH3
+H
H
OO
OO
H
H
CH2
CH2
CH2
NN
NH2
+
OO
NH3
+H
HH
OO
OO
H
CH2
CH2
CH2
CH2
NH3
+
OO
NH3
+H
NH2
NH2
O
O P O
O
OO
CH2
CH2
CH2
NNH2
O
OO
NH3
+H
H
OO
OO
H
CH2
NH3
+
(1-3 in cytosol, 4in mitochondial matrix)
2 ~ P used2 ~ P used
5
Connection to Krebs CycleConnection to Krebs Cycle
• Fumarate is oxidized to oxaloacetate by Krebs cycle Fumarate is oxidized to oxaloacetate by Krebs cycle enzymes, producing NADH.enzymes, producing NADH.
• Oxaloacetate accepts an amino group instead of Oxaloacetate accepts an amino group instead of being condensed with acetyl CoA.being condensed with acetyl CoA.
• Fumarate is oxidized to oxaloacetate by Krebs cycle Fumarate is oxidized to oxaloacetate by Krebs cycle enzymes, producing NADH.enzymes, producing NADH.
• Oxaloacetate accepts an amino group instead of Oxaloacetate accepts an amino group instead of being condensed with acetyl CoA.being condensed with acetyl CoA.
aspartate
fumaratearginine
argininosuccinate
citrulline
UREACYCLE
1
2
Malate
Oxaloacetate
-amino acid
-keto acid
NAD+
NADH
ATP+
AMP + PPi+
2 Pi
H20
6
Amino Acids to UreaAmino Acids to Ureaaminoacid
-ketoacid
carbamoylphosphate
ornithine UREACYCLE
glutamate
-ketoglutate
NH4+ + CO2
+ 2 ATP + H2O
2 ADP + Pi + H+ +
H2OUREA
NH2
NH2
O
*
aspartate
fumaratearginine
argininosuccinate
citrulline
Malate
Oxaloacetate
amino acid
-keto acid
AMP + PPi+
2 Pi
ATP+
**Glutamate Dehydrogenase is the control site: ADP (+), Glutamate Dehydrogenase is the control site: ADP (+), GDP (+), ATP (-), GTP (-) and NADH (-). GDP (+), ATP (-), GTP (-) and NADH (-).
Control at other sites by glucagon (+), cortisol (+), insulin Control at other sites by glucagon (+), cortisol (+), insulin (-), growth hormone (-).(-), growth hormone (-).
**Glutamate Dehydrogenase is the control site: ADP (+), Glutamate Dehydrogenase is the control site: ADP (+), GDP (+), ATP (-), GTP (-) and NADH (-). GDP (+), ATP (-), GTP (-) and NADH (-).
Control at other sites by glucagon (+), cortisol (+), insulin Control at other sites by glucagon (+), cortisol (+), insulin (-), growth hormone (-).(-), growth hormone (-).7
Summary of Reactions and Energetics - 1Summary of Reactions and Energetics - 1
HH220 + aa + NAD0 + aa + NAD++ -keto acid + NH-keto acid + NH44++ + NADH + H + NADH + H++
and and
HH220 + fumarate + aa + NAD0 + fumarate + aa + NAD++ aspartate + aspartate + -keto acid -keto acid + NADH + H+ NADH + H++
then then
aspartate + NHaspartate + NH44++ + HCO + HCO33
-- + 3 ATP + 3 ATP urea + fumarate + 2 Hurea + fumarate + 2 H220 + 2 ADP + AMP + 4 Pi + H0 + 2 ADP + AMP + 4 Pi + H+ +
Four high energy phosphate bond equivalents are used Four high energy phosphate bond equivalents are used for these reactions (- 4 ~P).for these reactions (- 4 ~P).Two NADH are produced.Two NADH are produced.
HH220 + aa + NAD0 + aa + NAD++ -keto acid + NH-keto acid + NH44++ + NADH + H + NADH + H++
and and
HH220 + fumarate + aa + NAD0 + fumarate + aa + NAD++ aspartate + aspartate + -keto acid -keto acid + NADH + H+ NADH + H++
then then
aspartate + NHaspartate + NH44++ + HCO + HCO33
-- + 3 ATP + 3 ATP urea + fumarate + 2 Hurea + fumarate + 2 H220 + 2 ADP + AMP + 4 Pi + H0 + 2 ADP + AMP + 4 Pi + H+ +
Four high energy phosphate bond equivalents are used Four high energy phosphate bond equivalents are used for these reactions (- 4 ~P).for these reactions (- 4 ~P).Two NADH are produced.Two NADH are produced.
8
Summary of Reactions and Energetics - 2Summary of Reactions and Energetics - 2
Now consider NADH oxidation:Now consider NADH oxidation:
2 H2 H++ + 2 NADH + O + 2 NADH + O22 2 NAD2 NAD++ + 2 H + 2 H220 (+5 ~P)0 (+5 ~P)
The net reaction is thenThe net reaction is then
2 aa + HCO2 aa + HCO33-- + O + O22
2 2 -keto acid + urea + H-keto acid + urea + H++ + 2 H + 2 H220 (+1~P) 0 (+1~P)
Now consider NADH oxidation:Now consider NADH oxidation:
2 H2 H++ + 2 NADH + O + 2 NADH + O22 2 NAD2 NAD++ + 2 H + 2 H220 (+5 ~P)0 (+5 ~P)
The net reaction is thenThe net reaction is then
2 aa + HCO2 aa + HCO33-- + O + O22
2 2 -keto acid + urea + H-keto acid + urea + H++ + 2 H + 2 H220 (+1~P) 0 (+1~P)
9
HyperammonemiaHyperammonemia
• Normal blood [NHNormal blood [NH44++] is 10-40 ] is 10-40 M.M.
• Deficiencies of carbamoyl phosphate synthetase or Deficiencies of carbamoyl phosphate synthetase or of any enzyme in the urea cycle cause high [NHof any enzyme in the urea cycle cause high [NH44
++].].
• Affects CNS and can lead to irreversible brain Affects CNS and can lead to irreversible brain damage.damage.
• Treatment strategies depend on which enzyme is Treatment strategies depend on which enzyme is deficient.deficient.
• Normal blood [NHNormal blood [NH44++] is 10-40 ] is 10-40 M.M.
• Deficiencies of carbamoyl phosphate synthetase or Deficiencies of carbamoyl phosphate synthetase or of any enzyme in the urea cycle cause high [NHof any enzyme in the urea cycle cause high [NH44
++].].
• Affects CNS and can lead to irreversible brain Affects CNS and can lead to irreversible brain damage.damage.
• Treatment strategies depend on which enzyme is Treatment strategies depend on which enzyme is deficient.deficient.
10
Argininosuccinase DeficiencyArgininosuccinase Deficiency• Low dietary protein Low dietary protein reduces need for urea reduces need for urea cycle.cycle.
• Low dietary protein Low dietary protein reduces need for urea reduces need for urea cycle.cycle.
• High dietary arginine High dietary arginine provides a path for provides a path for carbamoyl phosphate carbamoyl phosphate and aspartate and aspartate nitrogens to produce nitrogens to produce argininosuccinate, argininosuccinate, which is excreted.which is excreted.
• High dietary arginine High dietary arginine provides a path for provides a path for carbamoyl phosphate carbamoyl phosphate and aspartate and aspartate nitrogens to produce nitrogens to produce argininosuccinate, argininosuccinate, which is excreted.which is excreted.
ATP
AMP + PPi
H2O
+
+
aspartate
UREA
carbamoylphosphate
fumarate
arginine
argininosuccinate
ornithine
citrulline
UREACYCLE
1
23
4
2 Pi
H2N
CH2
CH2
CH2
NNH2
NH2
+
OO
NH3
+H
H
OO
OO
H
H
CH2
CH2
CH2
NN
NH2
+
OO
NH3
+H
HH
OO
OO
H
CH2
CH2
CH2
CH2
NH3
+
OO
NH3
+H
NH2
NH2
O
O P O
O
OO
CH2
CH2
CH2
NNH2
O
OO
NH3
+H
H
OO
OO
H
CH2
NH3
+
(excreted)
(excess supplied)11
Carbamoyl Phosphate Synthetase DeficiencyCarbamoyl Phosphate Synthetase Deficiency
• Hippurate and phenylacetylglutamine are excreted.Hippurate and phenylacetylglutamine are excreted.• Amino groups to glycine and glutamine by transamination.Amino groups to glycine and glutamine by transamination.
• Hippurate and phenylacetylglutamine are excreted.Hippurate and phenylacetylglutamine are excreted.• Amino groups to glycine and glutamine by transamination.Amino groups to glycine and glutamine by transamination.
12
Fig. 23.20
Ketogenic and Glucogenic Amino AcidsKetogenic and Glucogenic Amino Acids
• After removal of the amino group, the keto acids are used to make After removal of the amino group, the keto acids are used to make Krebs cycle intermediates, pyruvate, acetyl CoA and acetoacetyl CoA.Krebs cycle intermediates, pyruvate, acetyl CoA and acetoacetyl CoA.
• After removal of the amino group, the keto acids are used to make After removal of the amino group, the keto acids are used to make Krebs cycle intermediates, pyruvate, acetyl CoA and acetoacetyl CoA.Krebs cycle intermediates, pyruvate, acetyl CoA and acetoacetyl CoA.13
Fig. 23.21
Nitrogen for Oral BacteriaNitrogen for Oral Bacteria
• Urea is a major source of nitrogen for oral Urea is a major source of nitrogen for oral bacteria.bacteria.
• It diffuses through most membranes and is It diffuses through most membranes and is in saliva.in saliva.
• Bacterial urease produces NHBacterial urease produces NH44++..
• Glutamate dehydrogenase incorporates Glutamate dehydrogenase incorporates NHNH44
+ + into into -keto acids to obtain-keto acids to obtainamino amino
acids for bacterial growth.acids for bacterial growth.
• Urea is a major source of nitrogen for oral Urea is a major source of nitrogen for oral bacteria.bacteria.
• It diffuses through most membranes and is It diffuses through most membranes and is in saliva.in saliva.
• Bacterial urease produces NHBacterial urease produces NH44++..
• Glutamate dehydrogenase incorporates Glutamate dehydrogenase incorporates NHNH44
+ + into into -keto acids to obtain-keto acids to obtainamino amino
acids for bacterial growth.acids for bacterial growth.
H2NCONH2 + H+ + H2O 2 NH4+ + HCO3
-urease
14
Nitrogen for Bacterial Amino Acid SynthesisNitrogen for Bacterial Amino Acid Synthesis
glutamate
+ NH4+ glutamine
glutamine synthase
ATP ADP + Pi
-ketoglutarate+ glutamine 2 glutamate
glutamate synthase
NADPH + H+ NADP+
-ketoglutarate
+ NH4+
glutamate glutamate
dehydrogenase
NADPH + H+ NADP+
+ H20
• When [NHWhen [NH44++] is limiting, it does not bind glutamate dehydrogenase, and the ] is limiting, it does not bind glutamate dehydrogenase, and the
lower two reactions are used.lower two reactions are used.• When [NHWhen [NH44
++] is limiting, it does not bind glutamate dehydrogenase, and the ] is limiting, it does not bind glutamate dehydrogenase, and the lower two reactions are used.lower two reactions are used.15
Engineered Oral Bacteria to Fight Caries?Engineered Oral Bacteria to Fight Caries?
• Streptococcus Salivarius urease activity affects Streptococcus Salivarius urease activity affects oral microbial ecology.oral microbial ecology.
• It produces NHIt produces NH33, which in addition to promoting , which in addition to promoting
growth, neutralizes acids produces by other growth, neutralizes acids produces by other bacteria.bacteria.
• S. Salivarius urease gene was introduced into S. Salivarius urease gene was introduced into Streptococcus mutans GS5. It was expressed Streptococcus mutans GS5. It was expressed and during glucose metabolism reduced pH and during glucose metabolism reduced pH decrease and duration.decrease and duration.
• (Clancy & Burne,1997 FEMS Microbiol Lett 151:205)(Clancy & Burne,1997 FEMS Microbiol Lett 151:205)
• Streptococcus Salivarius urease activity affects Streptococcus Salivarius urease activity affects oral microbial ecology.oral microbial ecology.
• It produces NHIt produces NH33, which in addition to promoting , which in addition to promoting
growth, neutralizes acids produces by other growth, neutralizes acids produces by other bacteria.bacteria.
• S. Salivarius urease gene was introduced into S. Salivarius urease gene was introduced into Streptococcus mutans GS5. It was expressed Streptococcus mutans GS5. It was expressed and during glucose metabolism reduced pH and during glucose metabolism reduced pH decrease and duration.decrease and duration.
• (Clancy & Burne,1997 FEMS Microbiol Lett 151:205)(Clancy & Burne,1997 FEMS Microbiol Lett 151:205)
16
Web linksWeb links
Nitrogen Fixation. A summary of the topic.. A summary of the topic.
Nitrogen Cycle. The biological big picture.. The biological big picture.
Amino Acid Metabolism. Reviews reactions.. Reviews reactions.
Next topic:Next topic: Porphyrins, heme, Porphyrins, heme, bile pigmentsbile pigments
Web linksWeb links
Nitrogen Fixation. A summary of the topic.. A summary of the topic.
Nitrogen Cycle. The biological big picture.. The biological big picture.
Amino Acid Metabolism. Reviews reactions.. Reviews reactions.
Next topic:Next topic: Porphyrins, heme, Porphyrins, heme, bile pigmentsbile pigments