Easy to understand presentation for transamination

1. METABOLISM OF
PROTEINS AND AMINO
ACIDS
Prepared by : Rabia Khan Baber
Course Title : Biochemistry
Topic : Transamination

2. AIMS AND OBJECTIVES
Introduction to amino acid pool
Essential and nonessential amino acids
What is amino acid metabolism
Where does amino acid metabolism occur ?
The general ways of amino acids degradation
Outline of amino acid degradation
Transamination
Specific transaminases
Role of pyridoxal phosphate

3. AMINO ACID POOL
The amino acids available for protein synthesis at any given time; the
liver regulates the blood level of amino acids based on tissue needs
and converts excess amino acids to carbohydrates for energy
production.
The "Amino Acid Pool" is a grand mixture of amino acids available in
the cell derived from dietary sources or the degradation of protein.
Since proteins and amino acids are not stored in the body, there is a
constant turnover of protein.

4. NONESSENTIAL VS. ESSENTIAL
AMINO ACIDS
Nonessential AA
Amino acids that can be
synthesized by the body
Alanine, Asparagine, Aspartate,
Cysteine, Glutamate, Glutamine,
Glycine, Proline, Serine, Tyrosine
Essential AA
Amino acids that cannot be
synthesized by the body
Arginine, Histidine, Isoleucine,
Leucine, Lysine, Methionine*,
Phenylalanine*, Threonine,
Tryptophan, Valine

5. WHERE DOES AMINO ACID
METABOLISM OCCUR ?
The small intestines, liver, kidneys, and muscle are organs that play an
essential role in amino acid metabolism. The main role of each is given
as follows.
Intestine:
Amino acids from protein digestion are absorbed in the small
intestine.
Liver:
The catabolism of amino acids, except those with branched chains,
starts in the liver.
Kidney:
Kidney captures glutamine released from muscles.

6. AMINO ACID METABOLISM
 The general ways of amino acids degradation :
1. Transamination
2. Deamination
3. Decarboxylation

7. OUTLINE OF AMINO ACID
DEGRADATION
All amino acids contain at least one nitrogen atom, which forms their
α-amino group; several amino acids contain additional nitrogen atoms
in their side chains. Some nitrogen is used in biosynthesis, for example
of nucleotides, but most of it is surplus and must be eliminated. To this
end, the liver incorporates it into urea, which is released into the
bloodstream and excreted by the kidneys.
Removal of nitrogen is typically an early step in the degradation and
leaves behind the carbon skeleton. The structure of the latter is
different for each amino acid, and accordingly each amino acid has its
own specific pathway of degradation.

8. Cont..
The liver is the major site of degradation for most amino acids, but
muscle and kidney dominate the degradation of specific ones
Nitrogen is removed from the carbon skeleton and transferred to α-
ketoglutarate, which yields glutamate
The carbon skeletons are converted to intermediates of the mainstream
carbon oxidation pathways via specific adapter pathways
Surplus nitrogen is removed from glutamate, incorporated into urea,
and excreted

9. TRANSAMINATION
One of the central reactions of the amino acid metabolism is The
process of transamination occurs through aminotransferase enzymes
which can be specific for an amino acid or can cater to several amino
acids that are similar in their chemical compositions. Amino acid that is
currently not needed can be transformed into another amino acid that is
currently needed. The reallocation of the amino group occurs via an
alpha-keto acid, which has an analogous structure to alpha-amino acids.
Alpha-keto acids only differ from alpha-amino acids in having a keto
group, instead of an amino group.

10. α-amino acid
(Donor)
α-ketoacid
(Recipient)
New amino
acid
New keto acid

11. Transamination turns the alpha-keto acid into a new amino acid
available for metabolism. The responsible enzyme is called
aminotransferase (or transaminase). The aminotransferase, however,
needs an assistant to do its work: the pyridoxal phosphate (PLP). This
is a coenzyme produced out of vitamin B6 (pyridoxine) by
phosphorylation. PLP has an aldehyde group (H-C=O) that reacts in
the transamination with the amino group of the amino acid (with the
elimination of H2O). With this, a Schiff base (R-NH2) is formed. This
reaction destabilizes the amino acid and the hydrogen atom starts to
migrate which, in turn, leads to a shift of the double bond and
ketamine (R-C=O) emerges from the former aldimine (H-C=O).
Then, water is added across this double bond which concludes the
formation of the alpha-keto acid. PLP is reduced to PMP
(pyridoxamine phosphate). The reverse reaction is also a common
variation for generating another amino acid: pyridoxamine phosphate
reacts with another alpha-keto acid and PLP is reconstituted.

12. SPECIFIC TRANSAMINASES
Specific transaminases are clinically important because they use specific
amino acid and specific ketoacid.
i. Aspartate
transaminase
ii. Alanine
transaminase

13.  Aspartate transaminase (ASAT) ;
Also known as Aspartate amino transferase. The ASAT transfers the
amino group from aspartate to alpha-ketoglutarate, forming
oxaloacetate and glutamate.
 Alanine transaminase (ALT) ;
Also known as Alanine amino transferase. ALAT catalyzes the
transfer of an amino group from alanine to alpha-ketoglutarate,
forming pyruvate and glutamate

14. ROLE OF PYRIDOXAL PHOSPHATE IN
TRANSAMINATION
The pyridoxal phosphate, is the most important coenzyme in the amino
acid metabolism. PLP is the biologically active form of pyridoxal, the
aldehyde form of vitamin B6. Vitamin B6 also appears as amine
(pyridoxamine) and alcohol (pyridoxine). The derivatives of vitamin B6
can be converted into each other. They are ingested and can be found in
animal-based food (pyridoxal and pyridoxine), as well as in vegetable-
based food (pyridoxine). Wheat germs are relatively rich in vitamin B6.
PLP as a coenzyme is involved in the amino acid metabolism in the
reactions of transamination, decarboxylation and deamination.