Amino acid metabolism | Transamination | Deamination |

This PPT is on Amino acid metabolism. And the topics covered under this ppt are Transamination, deamination

Book referred: https://www.amazon.in/Biochemistry-2019-Satyanarayana-Satyanarayana-Author/dp/B07WGHCTKZ/ref=sr_1_1?dchild=1&qid=1591608419&refinements=p_27%3AU+Satyanarayana&s=books&sr=1-1

2. General Aspects on Metabolism of amino acids
The amino acids undergo certain common reactions like
transaminationfollowed by deaminationfor the liberation of
ammonia.
Theamino group of the amino acids is utilized for the formation of
urea which is an excretory end product of protein metabolism. urea which is an excretory end product of protein metabolism.
The carbon skeleton of the amino acids is first converted to ketoacids
(by transamination) for the following fates:
1. Utilized to generate energy.
2. Used for the synthesis of glucose.
3. Diverted for the formation of fat or ketonebodies.
4. Involved in the production of non-essential amino acids.

4. Transamination
The transfer of an amino (NH2) group from an
amino acid to a ketoacid is known as
transamination. transamination.
In this process the interconversionof a pair of
amino acids and a pair of ketoacids takes
place which is catalysedby transaminases.

5. Salient features of transamination
1. All transaminasesrequire pyridoxalphosphate (PLP), a coenzyme
derived from vitamin B6.
2. Only two transaminasescontribute for transaminationi.e.
aspartatetransaminaseand alaninetransaminase.
3. No free NH3 liberated, only the transfer of amino group occurs.3. No free NH3 liberated, only the transfer of amino group occurs.
4. Transaminationis reversible.

6. 5. It is important for the redistribution of amino groups and production of
non-essential amino acids. Involves both catabolism and anabolism.
6. Transaminationdiverts the excess amino acids towards energy
generation.
7. The amino acids undergo transaminationto finally concentrate nitrogen
in glutamate. Glutamate is the only amino acid that undergoes oxidative
deaminationto liberate free NH3 for urea synthesis.deaminationto liberate free NH3 for urea synthesis.
8. All amino acids participate in transamination.
Exception:lysine, threonine, prolineand hydroxyproline.
9. Transaminationis not restricted to α-amino groups only. For instance, δ-
amino group of ornithineis transaminated.
10. Serum transaminases: Important for diagnostic &prognostic purposes.

7. Mechanism of transamination
Transaminationoccurs in two stages
1. Transfer of the amino group to the coenzyme
pyridoxalphosphate to form pyridoxaminepyridoxalphosphate to form pyridoxamine
phosphate.

9. 2. The amino group of pyridoxaminephosphate is then
transferred to a ketoacid to produce a new amino acid
and the enzyme with PLP is regenerated.
All the transaminasesrequire pyridoxalphosphate (PLP).
Thealdehydegroup of PLP is linked with ε-amino group
of lysine residue, at the active site of the enzyme
forming a Schiff base. forming a Schiff base.
When an amino acid (substrate) comes in contact with
the enzyme, it displaces lysine and a new Schiff base
linkage is formed. The amino acid-PLP-Schiff base
tightly binds with the enzyme by noncovalentforces.

11. Deamination
•The removal of amino group from the amino acids as
NH3 is deamination.
•Deaminationresults in the liberation of ammonia for
urea synthesis. And the carbon skeleton of amino acids is urea synthesis. And the carbon skeleton of amino acids is
converted to ketoacids.
•Deaminationmay be either Oxidative orNon-Oxidative.
•Transaminationand deaminationoccur simultaneously,
often involving glutamate as the central molecule.

12. Oxidative deamination
•Oxidative deaminationis the liberation of free
ammonia from the amino group of amino acids
coupled with oxidation.
•Thisoccursin liver and kidney.
•The purpose of oxidative deaminationis to provide
NH3 for urea synthesis and α-ketoacids for a variety
of reactions, including energy generation.

13. Role of glutamate dehydrogenase:
In the process of transamination, the amino groups of most
amino acids are transferred toα -ketoglutarateto produce
glutamate. Glutamate rapidly undergoes oxidative
deamination, catalysedby glutamate dehydrogenase
(GDH) to liberate ammonia.
Conversion of glutamate to α -ketoglutarateoccurs through Conversion of glutamate to α -ketoglutarateoccurs through
the formation of an intermediate,α -iminoglutarate.
Glutamate dehydrogenasecatalysedreaction is important as
it reversibly links up glutamate metabolism with TCA cycle
through α -ketoglutarate.

14. Regulation of GDH activity:
•GTP and ATP inhibitglutamate dehydrogenase
•GDP and ADP activateglutamate dehydrogenase.
•Steroid and thyroid hormones inhibitGDH.
After a protein-rich meal, liver glutamate level is increased. It •After a protein-rich meal, liver glutamate level is increased. It
is converted to α-ketoglutaratewith liberation of NH3.
•And when the cellular energy levels are low, the degradation
of glutamate is increased to provide α-ketoglutaratewhich
enters TCA cycle to liberate energy.

15. Oxidative deaminationby amino acid oxidases:
L-Amino acid oxidase and D-amino acid oxidaseact on the
corresponding amino acids (L or D) to produce α-ketoacids
and NH3.
In this reaction, oxygen is reduced to H2O2, which is later
decomposed by catalase.decomposed by catalase.

16. Non-oxidative deamination
Some amino acids can be deaminatedwithout undergoing
oxidation:
•Amino acid dehydrases:Serine, threonineand
homoserineare the hydroxyamino acids. They undergo homoserineare the hydroxyamino acids. They undergo
non-oxidative deaminationcatalysedby PLP-dependent
dehydrases.

17. •Amino acid desulfhydrases:The sulfur amino
acids, namely cysteineand homocysteine,
undergo deaminationcoupled with
desulfhydrationto give ketoacids.

18. •Deaminationof histidine:The enzyme
histidaseacts on histidineto liberate NH3 by a
non-oxidative deaminationprocess.