Amino acid pool, Transamination, Deamination, Urea cycle, Ammonia metabolism

1. MetabolismMetabolism
ofof
ProteinProtein
Dr Ifat Ara Begum
Associate Professor
Dept of Biochemistry
Dhaka Medical College
Dhaka
1

2. What is metabolism?What is metabolism?
2
Metabolism is the
sum total of all the
chemical
reactions in the
body.

3. 3

4. 4

5. Protein TurnoverProtein Turnover
5

6. 6

7. What is Amino Acid Pool?What is Amino Acid Pool?
7
 The free amino acid content distributed
throughout the extracellular fluid
 Quantitatively, it is about 100 gm in
an adult individual.
 50% : Glutamate & Glutamine
 10% : EAA
 40% : Other AAs

8.
8

9. Intermediary metabolism of AminoIntermediary metabolism of Amino
acidacid
9
Anabolism Catabolism
 Synthesis of:
 NEAA
 Protein
NPN subs
Urea from NH3 via
urea cycle
 Glucose, glycogen
 FA, fat, steroid,
ketone bodies
 Transamination
 Deamination & removal
of NH2 group as NH3
 Catabolism of AA C-
skeleton & synthesis of
glucose, FA, steroids,
ketone bodies, etc.
 Oxidation of AA C-
skeleton via TCA cycle

10.
10
Transamination

11. What is Transamination?What is Transamination?
11
 It is the transfer of NH2 group from an
AA to a keto acid with simultaneous
production of a corresponding keto
acid & AA respectively.
Remember,
No free NH3 is produced here
Only transfer of NH2 group occurs

12. 12
Amino acid participating
in transamination
Keto acid participating
in transamination
All Amino acids except :
 Lys
 Thr
 Pro
Three keto acids
mostly participates:
 α- ketoglutarate
Oxaloacetate
 Pyruvate

13. 13

14. 14

15. Site of TransaminationSite of Transamination
15
Cytoplasm of:
 Liver
 Kidney
 Heart
 Sk. Muscle
 Brain.

16. Coenzyme needed for TransaminationCoenzyme needed for Transamination
16
Pyridoxal phosphate:
Acts as an intermediate carrier of an
NH2 group.

17. Importance of TransaminationImportance of Transamination
17
 Funneling of NH2 group of diff AAs
ultimately to α-KG :
To form Glu which is the major AA
that undergoes oxidative deamination.
 Biosynthesis of NEAA
 Formation of keto acid of an amino
acid:
Keto acid (carbon skeleton of AA)
later on can be catabolized/oxidized

18. 18
 Provides a link b/w carbohydrate,
protein & fat metabolism:
Because, the keto acids generated by
transamination of AA can form
compounds common to their metabolic
cycle.

19.
19
Oxidative
Deamination

20. What is Deamination?What is Deamination?
20
 Removal of –NH2 group from an AA in
the form of “free NH3 “
with simultaneous formation of its
corresponding keto acid.

21. AA unique in the process of DeaminationAA unique in the process of Deamination
21
Glutamate
Because,
it undergoes rapid oxidative
deamination catalyzed by
Glutamate dehydrogenase
(an active dehydrogenase)

22. 22

23. Site of DeaminationSite of Deamination
23
Mitochondria of:
 Liver
 Kidney
 Heart
 Sk. Muscle

24. Coenzyme needed for DeaminationCoenzyme needed for Deamination
24
NAD

25. Transamination vs. DeaminationTransamination vs. Deamination
25

26.
26
Sources & Fates
of Ammonia

27. 27
Sources of NH3 Fates of NH3
 Catabolism of :
 Amino acid
 Purine & Pyrimidine
 Bacterial degradation
of urea into NH3 by
bacterial urease in
intestinal lumen
 Formation of :
 Urea (Urea cycle)
 Glutamate &
Glutamine in liver,
kidney, muscle, brain
 Excretion of NH3 with
urine as NH4+ salt

28. 28
Glutamine :
The temporary non-toxic
storage & transport form of
NH3.
NH3 + α-KG  Glutamate
Glutamate + NH3 
Glutamine

29. Ammonia IntoxicationAmmonia Intoxication
29

30.
30
Urea cycle

31.
31

32. 32

33. Nitrogen BalanceNitrogen Balance
33

34. Inborn error of protein metabolismInborn error of protein metabolism
34
 Alkaptonuria
 Homocystinuria
 Phenylketonuria
 Albinism
 Maple syrup urine disease

35. 35