Nitrogen assimilation, nitrogen balance, nitrogenous wastes and formation of nitrogenous wastes

1. ASSIMILATION OF NITROGEN WITH REFERENCE TO
AMMONIA, UREA, URIC ACID, CREATINE AND CREATININE
HEMA T
MSc BIOCHEMISTRY
BHARATHIAR UNIVERSITY

2. NITROGEN
 Nitrogen is a very important constituent of cellular components.
 Alkaloids, amides, amino acids, proteins, DNA, RNA, enzymes, vitamins,
hormones and many other cellular compounds contain nitrogen as one of the
elements.
 Nitrogen is the key element for it is the most important constituent of
proteins and nucleic acids.
 Thus N2 plays a significant role in the formation of the above said
compounds.
 Without nitrogen, no living organism can survive.

3. NITROGEN ASSIMILATION
 Nitrogen assimilation is defined as the incorporation of
Nitrogen into organic compounds, and for the purpose of
formation of amides and amino acids from keto acids and NH3.

4. NITROGEN BALANCE
 In an adult healthy individual maintaining constant weight, the
amount of intake of N in food (mainly as dietary proteins) will be
balanced by an excretion of an equal amount of N in urine (in form
of urea mainly, uric acid, creatinine/and creatine, and amino acids
contribute to a minor extent) and in faeces (mainly as unabsorbed
N). The individual is then said to be in nitrogen balance or
nitrogenous equilibrium.

5. +VE AND –VE NITROGEN BALANCE
 If intake of N is greater than the output, it is said to have a +ve
nitrogen balance.
In the growing period and also during convalescence from illness or when
anabolic hormones are given, the body puts on weight and N-intake will be
more than N-output, since some of the N is retained as tissue proteins.
 If intake of N is less than the output of N, it is said to have a –ve
nitrogen balance.
In old age and during illness and starvation weight is lost and results in –ve
nitrogen balance.

6. NITROGENOUS WASTES
 The nitrogen compounds through which excess nitrogen is
eliminated from organisms are called nitrogenous wastes
or nitrogen wastes.
 They are
 ammonia
 urea
 uric acid
 creatine and
 creatinine.

7. FORMATION OF AMMONIA
In mammalian tissues, α-NH2 group of amino acids, derived either
from the diet or breakdown of tissue proteins, ultimately is
converted first to NH3 and then to urea and is excreted in the urine.

8. FORMATION OF AMMONIA…
Formation of NH3 and urea can be discussed under the
following heads:
 Transamination
 Deamination
 Oxidative deamination
 Non-oxidative deamination
 Transdeamination

9. TRANSAMINATION
 It was first discovered by Braunstein and Kritzmann (1947).
 It is a process of combined deamination and amination.
 Definition: Transamination is a reversible reaction in liver in which
α-NH2 group of one amino acid is transferred to a α-ketoacid
resulting in formation of a new amino acid and a new ketoacid.

10. TRANSAMINATION…
 The process represents only an intermolecular transfer of NH2 group
without the splitting out of NH3. Ammonia formation does not take place
by transamination reaction.
The general process of transamination may be represented as follows:

11. DEAMINATION
 Deamination is the process by which N– of amino acid is removed as NH3.
Types: It can be of 2 types:
A. Oxidative deamination
B. Non-oxidative deamination.

12. OXIDATIVE DEAMINATION
 Site of oxidative deamination: Krebs (1935) studied
deamination of amino acids in various tissue slices and found that
liver and kidney to be very active.

13. OXIDATIVE DEAMINATION…

14. NON-OXIDATIVE DEAMINATION
Amino acid dehydrases

15. NON-OXIDATIVE DEAMINATION…
Histidase

16. NON-OXIDATIVE DEAMINATION…
Amino acid desulfhydrases

17. TRANSDEAMINATION
 Deamination of L-Glutamic Acid
Deamination takes place
primarily in the liver, however
glutamate is also deaminated in
the kidneys.

18. AMMONIA PRODUCTION BY INTESTINAL FLORA
 It is stressed that in addition to NH3 formed in the tissues, a
considerable quantity of NH3 is produced in the gut by intestinal
bacterial flora, both
• From dietary proteins, and
• From urea present in fluids secreted into the GI tract.

19. UREA FORMATION
(KREBS-HENSELEIT CYCLE)
 The removal of excess of NH3 derived from amino acid catabolism
in the tissues or from bacterial action in the gut is accomplished by
the production of urea which is excreted in the urine.
 Steps of urea synthesis in liver have been elucidated by Krebs and
Henseleit (1932).

20. KREBS-HENSELEIT CYCLE

21. REACTIONS OF UREA CYCLE
 The reactions of urea cycle can be studied in five sequential enzymatic
reactions.
• Reaction 1: Synthesis of carbamoyl-phosphate
• Reaction 2: Synthesis of citrulline
• Reaction 3: Synthesis of argininosuccinate
• Reaction 4: Cleavage of argininosuccinate
• Reaction 5: Cleavage of arginine to form ornithine and urea

22. SOURCE OF C AND N OF UREA
 One Nitrogen of NH2 group is derived from the NH+4 ion
(Reaction 1).
 Other Nitrogen of NH2 group is provided by Aspartate (Reaction
3).
 Bicarbonate, HCO–
3 ion, provides the carbon atom of urea.

23. FORMATION OF URIC ACID
 Uric acid is a product of the metabolic breakdown of purine
nucleotides, and it is a normal component of urine.
 High blood concentrations of uric acid can lead to gout and are
associated with other medical conditions, including diabetes and
the formation of ammonium acid urate kidney stones.

24. FORMATION OF URIC ACID…

25. CREATINE FORMATION
 Creatine is an organic compound with the nominal formula
(H2N)(HN)CN(CH3)CH2CO2H.
 Creatine synthesis primarily occurs in the liver and kidneys.
 Most of the human body's total creatine and phosphocreatine stores are
found in skeletal muscle, while the remainder is distributed in the blood, brain,
and other tissues.

26. CREATINE FORMATION…
 Creatine is found
in vertebrates where it
facilitates recycling
of adenosine triphosphate(ATP),
the energy currency of the cell,
primarily
in muscle and brain tissue.
Recycling is achieved by
converting adenosine
diphosphate(ADP) back to ATP
via donation of phosphate
groups.

27. CREATININE FORMATION…
 Creatinine is a waste product produced by muscles from the
breakdown of a compound called creatine.
 Creatinine is removed from the body by the kidneys, which filter
almost all of it from the blood and release it into the urine.

28. CREATINE AND CREATININE FORMATION…

29. CREATINE AND CREATININE FORMATION…

30. SUMMARY
 By the above mentioned processes the nitrogenous wastes like
ammonia, urea, uric acid, creatine and creatinine are formed. The
formed nitrogenous wastes are eliminated through urine and
feces excretion. The modes of excretion of nitrogenous wastes
are different in different organisms.

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