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Amino Acid Catabolism

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Amino Acid Catabolism Amino Acids essential - excess are converted to metabolic intermediates such as: pyruvate, acetyl-CoA and are precursors for fatty acids ... – PowerPoint PPT presentation

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Title: Amino Acid Catabolism


1
Amino Acid Catabolism
  • Amino Acids
  • essential - excess are converted to metabolic
    intermediates such as pyruvate, acetyl-CoA and
    are precursors for fatty acids, glucose, ketone
    bodies
  • 2. nonessential - biosynthesis
  •  
  • Amino Acid Breakdown (3 Stages)
  • 1. Deamination remove an amino group
  • 2. Incorporation of ammonia and aspartate
    nitrogen atoms into urea for excretion
  • 3. Conversion of amino acid carbon skeletons to
    common metabolic intermediates
  •      

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?-ketoglutarate and glutamate play central roles
in amino acid catabolism
4
Stage 1 Deamination -  Remove a-amino group
Purpose excrete excess nitrogen and degrade
the remaining carbon skeleton or convert it
to glucose Main way Transamination (2 Stages)
i.      AA enzyme ? a-keto acid
enzyme-NH2                 ii.     
a-ketoglutarate enzyme-NH2 ? enzyme
glutamate Enzyme requires PLP which acts as a
temporary store of amino groups until the next
substrate comes in. (ping-pong mechanism)
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Amino transferases
9
Now How do we get the amine group off of
glutamate?!?!? Oxidative deamination via
Glutamate dehydrogenase (GDH) -first committed
step on the pathway to nitrogen excretion -
instead of just swapping amino groups, there is
a NET LOSS of nitrogen GDH is unique because
it is one of the only enzymes that does not
discriminate between NAD and NADP
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  •      
  • Stage 2 of Amino Acid Breakdown
  • Incorporation of ammonia and aspartate nitrogen
    atoms into urea for excretion (The Urea Cycle)
  •  
  • Living organisms excrete excess nitrogen in 1 of
    3 ways.
  • as ammonia ex) aquatic animals
  • as urea ex) people
  • as uric acid ex) birds and reptiles
  •  
  • Urea is synthesized in your liver, secreted into
    the bloodstream and sequestered by the kidneys
    for excretion into the urine. Urea is very
    soluble, but still requires an appreciable amount
    of water to remove it from the kidneys. Why is it
    so vital to get rid of? Ammonium salts are toxic
    and can cause vomiting, convulsions and
    ultimately coma and death when the blood
    concentration exceeds 0.25 mM.

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Net Reactions
1Glutamate H2O NADP ---gt ?-KG NH4 NADPH
H
Aspartate NH3 3ATP H2O HCO3- ---gt 2ADP
AMP PPi 2Pi fumarate urea
fumarate NAD ---gt oxaloacetate NADH
1Glutamate oxaloacetate ---gt ?-KG aspartate
2 glutamate (NH3) HCO3- 3ATP NAD ---gt 2
?-KG urea 2ADP AMP 4Pi NADH
NADH 3ATP
17
Stage 3 Recycling the skeletons
18
Alanine the simplest case
Ala is glucogenic and pyruvogenic
Alanine aminotransferase
Per 2NH3 4 ATP are consumed by the urea cycle
Pyruvate
Degradation of alanine costs 2ATP!!
19
How then do we get energy out of pyruvate?
20
Pyruvate ---gt acetyl-CoA CO2 1 NADH
Isocitrate ---gt ?-ketoglutarate CO2 1 NADH
?-ketoglutarate ---gt succinyl-CoA CO2 1 NADH
Succinyl-CoA ---gt succinate 1 GTP
Succinate ---gt fumarate 1 FADH2
Malate ---gt oxaloacetate 1 NADH
21
So Pyruvate 4 NADH 1 FADH2 GTP
1 NADH 3 ATP 1 FADH2 2 ATP 1 GTP 1 ATP 1
NH3 -2 ATP
Then Pyruvate 15 ATP
If Ala pyruvate NH3
Then Ala 15 ATP - 2 ATP 13 ATP
22
Asparagine
asparaginase
aspartate aminotransferase
Aspartate
Oxaloacetate
23
Asp oxaloacetate NH3
Asn oxaloacetate 2NH3
How then do we get energy out of oxaloacetate? It
is not degraded by the TCA cycle!
24
Run malate dehydrogenase in reverse
Malate
Oxaloacetate
Loss of one NADH
25
Malic enzyme malate dehydrogenase,
decarboxylating
Malate
NADPH
NADP
Pyruvate
Malate dehydrogenase Malic enzyme Net
conversion of one NADH to one NADPH
Oxaloacetate NADH NADP ---gt pyruvate CO2
NAD NADPH
26
Sooxaloacetate pyruvate - NADH NADPH
If pyruvate 4 NADH 1 GTP 1 FADH2
Then oxaloacetate 3NADH GTP FADH2 NADPH
If Asp oxaloacetate NH3 and Asn
oxaloacetate 2 NH3
Then Asp 3 NADH GTP FADH2 NH3 NADPH
and Asn 3 NADH GTP FADH2 2 NH3 NADPH
If NADH 3 ATP GTP ATP FADH2 2 ATP NH3 -2
ATP
Then Asp 10 ATP NADPH and Asn 8 ATP NADPH
27
Glutamine
Glutaminase
Glutamate dehydrogenase
?-ketoglutarate
Glutamate
28
How do we get energy from ?-ketoglutarate?
29
If ?-ketoglutarate ---gt succinyl-CoA CO2 1
NADH
If Succinyl-CoA ---gt succinate 1 GTP
If Succinate ---gt fumarate 1 FADH2
Then ?-ketoglutarate to malate 1 NADH, 1 GTP,
1 FADH2
If malate to pyruvate converts NADH to NADPH
If Pyruvate 4 NADH 1 GTP 1 FADH2
Then ?-ketoglutarate 4NADH 2 GTP 2 FADH2
NADPH
30
So ?-ketoglutarate 4NADH 2 GTP 2 FADH2
NADPH
If Glu ?-ketoglutarate NH3 NAPDH and Gln
?-ketoglutarate 2 NH3 NAPDH
Then Glu 4 NADH 2GTP 2FADH2 NH3 2
NAPDH and Gln 4 NADH 2GTP 2FADH2 2NH3 2
NAPDH
If NADH 3 ATP GTP ATP FADH2 2 ATP NH3 -2
ATP
Then Glu 16 ATP 2 NADPH and Gln 14 ATP 2
NADPH
31
Alanine
Pyruvate NH3
Cysteine
Pyruvate S2- NH3
Serine
Pyruvate NH3
32
2 Glycine
Pyruvate CO2 2 NH3 NADH
Threonine glycine
Pyruvate Acetyl-CoA 2 NH3 CO2 2NADH
33
Aspartate
Oxaloacetate NH3
Asparagine
Oxaloacetate 2 NH3
Glutamate
?-ketoglutarate NH3 NADPH
Glutamine
?-ketoglutarate 2 NH3 NADPH
34
Arginine
?-ketoglutarate urea 2 NH3 2 NADPH
Proline
?-ketoglutarate NH3 2 NADPH
Histidine
?-ketoglutarate N5,N10-methenyl THF 3 NH3
NADPH
35
Methionine serine (Costs 3 extra ATP)
methylated acceptor 2 NH3 pyruvate S2-
NADH succinyl-CoA
Isoleucine (Costs 1 extra ATP)
Acetyl-CoA succinyl-CoA NH3 2 NADH FADH2
Valine (Costs 1 extra ATP)
Succinyl-CoA NH3 3 NADH FADH2
Leucine (Costs 1 extra ATP)
3 Acetyl-CoA NH3 NADH FADH2
36
Lysine
2 Acetyl-CoA 3 NADH 2 CO2 2 NH3
Tryptophan (Costs 2 NADPH)
Formate pyruvate 2 acetyl-CoA 2 NH3 3 CO2
NADH
Tyrosine (Costs ascorbate)
Fumarate 2 acetyl-CoA NH3 CO2
Phenylalanine (Costs ascorbate and NADPH)
Fumarate 2 acetyl-CoA NH3 CO2
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When there is lots of glucose
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When there is a glucose deficiency but plenty of
protein
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High fat diet
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The lipostat theory
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