Amino acid metabolism

metabolism of amino acid, urea cycle

1. AMINO ACID METABOLISM
Mrs. Kulkarni DipaliM.
Assistant Professor,
Yash Institute of Pharmacy,
Aurangabad.

2. Amino acid metabolism
General reactions of amino acid metabolism:
Transamination,
deamination
decarboxylation,
urea cycle and its disorders

3. Metabolism
•Total of all chemical changes that occur in
body.Includes:
–Anabolism: energy-requiring process where small
molecules joined toformlargermolecules
•E.g.Glucose+Glucose
–Catabolism: energy-releasing process where
large moleculesbroken down tosmaller
•Energy in carbohydrates, lipids, proteins is
used to produce ATP through oxidation-
reductionreactions

4. MetabolicPathways
•The enzymatic reactions of
metabolismformanetwork of
interconnected chemical reactions,
orpathways.
•The molecules of the pathway are
called intermediates because the
productsofonereactionbecome the
substrates of the next.
•Enzymescontrolthe flow ofenergy
throughapathway.
IntermediaryMetabolism

5. WHAT IS AMINO ACID?
Amino acids are derivatives of carboxylic acids formed by
substitution of α-hydrogen for amino functional group. Hence
all amino acids are α-Amino acid .
All naturally occurring amino acids are Levo -rotatory.
Amino acid Metabolism

6. WHAT DO AMINO ACIDS DO?
•Amino acids are essential to life, have a role in
metabolism,andare important in nutrition.
•They form short polymer chains called peptides, as well
as longer chains that are called polypeptides or proteins.
•About 75 percent of the human body is made up of
chains of amino acids, which is why they are so vital to
how your system functions.
•All the chemical reactions that occur in the body
depend on amino acids and the proteins they build.

7. TYPES OF AMINO ACIDS
Amino acids are classified as
Nonpolar(hydrophobic) with
hydrocarbon side chains.
Polar (hydrophilic) with polar
orionicside chains.
Acidic (hydrophilic) with acidic
side chains.
Basic (hydrophilic)
With –NH2 side chains.
Nonpolar
Nonpolar
Polar
Acidic
Basic

8. •Non-essential amino
acids
-can be synthesized
by an organism
-usually are prepared
from precursors in 1-2
steps
• Essential amino acids
-cannot be made
endogenously
-must be supplied in
diet
eg. Leu, Phe…..
Nutritionally Nonessential A A
: Alanine, glycine, aspartate,
glutamate, serine, tyrosine,
cysteine, proline,glutamine,
aspargine
Nutritionally-Essential amino
acids :Lysine, Leucine, Isoleucine,
Valine, Methionine,Phenylalanine,
Threonine, Tryptophan
N.B. Histidine& arginineare semi
essential. They are essential only for
infants growth, but not for old
children or adults
where in adults histidinerequirement is
obtained by intestinal flora & arginine
by urea cycle

9. METABOLIC FATES OF AMINO ACIDS:
1Bodyproteinbiosynthesis.
2Smallpeptide biosynthesis(GSH).
3-Synthesis
nitrogenous
ofnon-protein
(NPN)compounds(creatine,
urea,ammoniaanduricacid)
4-Deamination&Transaminationto
synthesizedanewaminoacidorglucoseor
ketonebodiesorproduceenergyinstarvation.

10. Sources&fates
ofaminoacids:
•Protein turnover :
(results from
simultaneoussynthesis
& breakdown of
proteinsmolecules)
•Totalamountofprotein
inbody of healthy adult
isconstant(due to rate
of protein synthesis is
equal to the rate of its
breakdown).
Bodyprotein
400gperday,synthesis
Bodyprotein
400gperday breakdown
Dietaryprotein
Synthesisnon-
essentiala.as.
Ketone bodies
Fattyacid&steroidsGL.&Glycogen
CO2&E

11. ProteinMetabolism
•Non-essentialaminoacidscanbeformedby
transamination,transferofanaminegroup
toketoacid.Canalsobeeaten.
•If used for energy, amino acids undergo
oxidative deamination. Ammonia and keto
acidsare producedasby-products of
oxidativedeamination.Ammoniais
convertedtoureaandexcreted.
•Aminoacidsarenot storedinthe body

13. *Metabolismofproteins isthemetabolism
ofaminoacids.
NH2 COOH
*Metabolismof aminoacidsisapartofthe
nitrogenmetabolisminbody.
*Nitrogenenters thebodyin dietaryprotein.
*Dietaryproteins cannotbe stored assuchbut
used forformation oftissueproteinsdue to
there isacontinuousbreakdownof
endogenoustissueproteins.

14. Sources&fates
ofaminoacids:
•Protein turnover :
(results from
simultaneoussynthesis
& breakdown of
proteinsmolecules)
•Totalamountofprotein
inbody of healthy adult
isconstant(due to rate
of protein synthesis is
equal to the rate of its
breakdown).
Bodyprotein
400gperday,synthesis
Bodyprotein
400gperday breakdown
Dietaryprotein
Synthesisnon-
essentiala.as.
Ketone bodies
Fattyacid&steroidsGL.&Glycogen
CO2&E

15. MetabolismOFAMINOACIDS:
R
1.Removal ofamoniaby: NH2CHCOOH
-Deamination Oxidativedeamination
1)glutamatedehydrogenaseinmitochondria
2)aminoacidoxidase inperoxisomes
Directdeamination(nonoxidative)
1)dea.bydehydration(-H2O)
2)dea. by desulhydration(-H2S)
-Transamination(GPT&GOT)
-andtransdeamination.
2.Fateofcarbon-skeletonsof aminoacids
3.Metabolismof ammonia

17. TheroleofPLPasCo-aminotransferase:
PLPbinds tothe enzyme viaschiff’sbase&ionic saltbridge&
helpsintransferofamino group betweenaminoacidandketo
acid(KG):
R
1
-CH-C O O H
NH
2
R
1
-CH-C O O H
N
CH
R
1
-C-C O O H
N
CHO
Enz
OH
CH
3
N
Enz
OH
CH
3
N
Enz
OH
3
HC
2
CHNH
2
R
2
NH
2
R
2
-C-C O O H
O
2
R-C-C O O H
N
N
Enz
OH
CH
3
(aminoacid)
PLP-Enz
2
HO
H
2O
H
2O
(ketoacid)H
2O
Pyridoxamine
Newketoacid
O
O
NH2
New(neawmaimnoinoaacciidd)
CH2
R1
R1 R1
R2
R2-CH-C O O H

18. Mechanism of transamination
All amino transferasesrequire the
prosthetic group pyridoxal
phosphate (PLP), which is derived
from pyridoxine (vitamin B6).
First step: the amino group of
amino acid is transferred to
pyridoxalphosphate, forming
pyridoxaminephosphate and
releasing ketoacid.
Second step: -ketoglutarate
reacts with pyridoxamine
phosphate forming glutamate

19. MetabolicSignificance ofTransamination
Reactions
➢Itisanexchangeofaminonitrogenbetween
themoleculeswithoutanetloss
➢Thismetabolicallyimportant because:
1)Thereisnomechanismforstorageofaprotein
oraminoacids.
2)Incaseoflowenergy(caloricshortage),the
organismdependsonoxidationofthe
ketoacidsderivedfromtransaminationofamino
acids.
3)Itisimportantforformationofthenon-essential
aminoacids

20. DeaminationofAminoAcids
a)OxidativeDeamination:
1)Glutamatedehydrogenase,mitochondrial,potent,major deaminase
Glutamat
NAD
orNADP
2
HO
Glu. dehydrogenase
NADH+H
+
NADPH+H
+
-ketoglutarate+NH
3
It is allostericallystimulatedbyADP&
inhibitedbyATP,GTP&NADH.
Thus,highADP(lowcaloric intake)increasesprotein degradation
highATP(wellfed-state)decreasesdeamination ofamino
acids&increasesprotein synthesis.
-NH3
-KetoacidAminoacid

21. 2)AminoAcidOxidases:
The minor pathway for deamination of amino acids.
Theyarefoundinperoxisomesofliverand kidney.
L-aminoacidoxidasesutilizeFMNwhileD-a.a.oxidases
utilizeFAD.
R
H-C-NH
2
COOH
R
C=NH
COOH
R
C=O
COOH
O
2
a.a.Oxidase
FMN FMNH
2
2
HO
NH
3
iminoacid ketoacid
Catalase
HO
22H
2O+O
2

22. •D-aminoacidoxidasesarehighlyactive
thanL-aminoacidoxidasesespeciallyin
kidneyandliverdueto:
thefunctionofD-aminoacidoxidasesis
therapidandirreversiblebreakdownofD-
aminoacidssince:
•D-aminoacidsarepotentinhibitorsto
L-aminoacidsoxidases

23. b)Non-oxidative deamination:
(DirectDeamination)
1)Deaminationbydehydration:
Serine&Threonine
CHOH
2
H-C-NH
2
COOH
PLP
CH
2
C-NH
2
COOH
CH
3
C=N H
C O O H
CH
3
HOOC -C=O
Serdehydratase
H
2O
H
2O
NH
3Pyruvate
Serine

24. 2)Deaminationbydesulfhydration:
(cysteine)
CH
2
SH
H-C-NH
2
COOH
PLP
CH
2
C-NH
2
COOH
CH
3
C=NH
COOH
HOOC-C=O
CH
3
Cys.desulfhydratase
2
HS
H
2O
NH
3Pyruvate
Cysteine

30. MetabolicDisposalofAmmonia
HOOC-CH
2
-CH
2
-CHCOOH
NH
2
NH
3
ATP ADP+Pi
H
2
N-C-CH
2
-CH
2
-CH-COOH
O NH
2
Glnsynthase
Mg
2+
Glutamate Glutamine
H2O
AmmoniaistoxictoCNS,itisfixedintonontoxicmetaboliteforreuseor
excretionaccording to thebodyneeds:
a)FormationofGlutamate:
-KG+NH
3
b)GlutamineFormation:Muscle,brain
Ketoacid
-Aminoacid
GDH T.A.
Glutamate
Glutamineisstorehouseofammonia&transporterformofammonia.
Inbrain,glutamineisthemajormechanismfor removalof ammonia
whileinliveris urea formation.
..Circulatingglutamineisremovedbykidney,liverandintestinewhereit is
deamidatedbyglutaminase.
c)Ureaformation

31. ..
Diet&body
protein
a.
Glu.
Biosynthesis
Ofpurine &
Pyrimidine
Urine
NH4+Urine
Kidney
Liver
Kidney
Glutaminase
Glutamine Glutamate+NH
3
H
2O
Thisreactionisimportanttokidneydue tokidneyexcretesNH
4iontokeep
+
extracellularNa
+
ioninbodyandtomaintaintheacid-basebalance.
Deaminase
GIT
Diet&Body
protein
glutamine
urea
Purines,pyrimidines
Various nitrogen-
containingcompounds
glutaminase
Bacterial
urease

32. c)UreaFormation
❖Urea is the principal end-product of
protein metabolismin humans.
❖It isimportantroutefordetoxicationofNH
3.
❖Itisoperatedinliver,releasedintobloodand
clearedbykidney.
❖Urea is highly soluble, nontoxic and has a high
nitrogencontent(46%), so…itrepresents about80-
90%ofthenitrogenexcretedinurineperdayinman
❖Biosynthesis of urea in man is an energy-requiring
process.
❖It takes place partially in mitochondria and
partiallyincytoplasm.

33. TheUrea
Cycle
(The
Ornithine
Cycle,
Kreb's
Henseleit
Cycle):
NAD
MDH
o
H2
Glu
Glu
NADH2

35. MetabolicSignificantAspectsof UreaCycle
A)EnergyCost:. Energycostofthecycleis onlyone ATP.
B)ureacycleisrelatedtoTCAcycle:
1.CO
2
2.Aspartate arises via transamination of oxaloacetate with
glutamate. Thus, depletion of oxaloacetate will decrease urea
formation(as inmalonatepoisoning).
3.Fumarateenters TCAcycle
C)SourcesofNitrogeninurea:free NH andaspartate.
3
N.B.glutamateistheimmediatesourceofbothNH
3(viaoxidative
deaminationbyGlu.Dehyd.)andaspartatenitrogen(through
transaminationofoxaloacetatebyAST).

36. ImportanceofUreaCycle
1.Formationofarginine(inorganisms
synthesizingarginine)&formationofurea(in
ureotelicorganisms,man)duetopresenceof
arginase.
2.Livershowsmuchhigheractivityofarginase
thanbrainorkidneyforformationofureawhile
inbrainorkidneyisthesynthesisofarginine.
3.Synthesisofnon-proteinaminoacids(ornithine
andcitrulline)inbody.

37. RegulationofUreaCycle
1)Activityof individualenzymes:
THERATE LIMITINGSTEPSa)carbamoylphosphatesynthase-1
b)Ornithinetranscarbamyolase.
c)Arginase.
❖N-acetylglutamateis activatorforcarbamoylphosphatesynthase-1
Itenhances itsaffinityforATP.
Itissynthesizedfrom acetyl CoA andglutamate.
itshepatic concentrationincreasesafter intake
ofaproteindiet,leading toanincreasedrate ofureasynthesis.
islimitedbythe❖Activityofornithinetranscarbamyolase
concentrationofitsco-substrate"ornithine".

38. 2)Regulationofthefluxthrough thecycle:
a)Fluxofammonia:
1.byaminoacids releasefrommuscle
(alanine, glutamine),
2.metabolism ofglutamineintheintestine
•
•
•
3.aminoacidsdegradationintheliver.
b)Availabilityofornithine.
c)Availabilityof aspartate:
since aspartateisrequiredinequimolaramountswithammonia,
this is satisfiedbyoftransdeamination .
3)ChangeinthelevelofEnzymes:
Arginase&otherurea-formingenzymesareadaptiveenzymes
thus
aprotein-richdietwillincreasetheirbiosynthesisrate&the
oppositeis trueforlowproteindiet.
However,in starvation,wherethebodyisforcedtouseitsowntissue
proteinas fuel,thereis anincreaseinurea-formingenzymes.

39. Detoxication of ammonia in the liver

41. (1)Hereditary Hyperammonemia(genetic deficiencies of Urea
cycle enzymes)
• Ornithinecarbamyltransferase(OTC) deficiency (X linked)
• Carbamylphosphate synthetaseI (CPS I) deficiency
• Citrullinemia( enzyme defect?)
• ArginosuccinicAciduria(enzyme defect? )
• Argininemia(not severe why?)(enzyme defect? )
• N-acetylGlusynthasedeficiency
(2) Acquired Hyperammonemia-------
a) Liver disease----(cirrhosis , hepatitis)
b) High protein diet
Clinical significance of blood urea:
• Elevated in renal insufficiency.
• Decreased in hepatic failure.